Karl Popper was "opposed to induction when it came to science"
To be precise, Popper was opposed to the view which equates the scientific method with inductive reasoning:
According to a widely accepted view — to be opposed in this book — the empirical sciences can be characterized by the fact that they use ‘inductive methods’, as they are called. According to this view, the logic of scientific discovery would be identical with inductive logic, i.e. with the logical analysis of these inductive methods. (From "The Logic of Scientific Discovery")
As for Notturno's comment in question:
Induction concerns itself entirely with justification
...this is a poetic phrasing (anthropomorphizing) as induction does not (read: cannot) "concern itself" with anything.
Without a subscription to philpapers.org and short of the funds for Mark Amadeus Notturno's book it might be helpful if you could provide some further context for his description of Popper's thought on induction? That said, the following quote from this review of Notturno's book might shed some light on the meaning regarding Notturno's comment that "induction concerns itself entirely with justification":
Notturno argues that the great failure of inductivists and institutionalists comes from the subjective justification: ‘they feel rational and hence justified, in believing that what they do, and because they infer from this that what they believe must be justified too’ (p. 88)
You might also find Notturno's "Popper And Hayek: On Democracy And Open Society" informs your reading of his meaning.
As for what Popper is aiming at, from his "Logic of Scientific Discovery" regarding induction and justification:
...it is far from obvious, from a logical point of view, that we are justified in inferring universal statements from singular ones, no matter how numerous; for any conclusion drawn in this way may always turn out to be false: no matter how many instances of white swans we may have observed, this does not justify the conclusion that all swans are white.
The question whether inductive inferences are justified, or under what conditions, is known as the problem of induction.
The problem of induction may also be formulated as the question of the validity or the truth of universal statements which are based on experience, such as the hypotheses and theoretical systems of the empirical sciences. For many people believe that the truth of these universal statements is ‘known by experience’; yet it is clear that an account of an experience—of an observation or the result of an experiment—can in the first place be only a singular statement and not a universal one.
For an example, from Popper's "Conjectures and Refutations":
I found that those of my friends who were admirers of Marx, Freud, and Adler, were impressed by a number of points common to these theories, and especially by their apparent explanatory power. These theories appeared to be able to explain practically everything that happened within the fields to which they referred. The study of any of them seemed to have the effect of an intellectual conversion or revelation, opening your eyes to a new truth hidden from those not yet initiated. Once your eyes were thus opened you saw confirming instances everywhere: the world was full of verifications of the theory. Whatever happened always confirmed it. Thus its truth appeared manifest; and unbelievers were clearly people who did not want to see the manifest truth; who refused to see it, either because it was against their class interest, or because of their repressions which were still 'un-analysed' and crying aloud for treatment.
The most characteristic element in this situation seemed to me the incessant stream of confirmations, of observations which 'verified' the theories in question; and this point was constantly emphasized by their adherents. A Marxist could not open a newspaper without finding on every page confirming evidence for his interpretation of history; not only in the news, but also in its presentation--which revealed the class bias of the paper--and especially of course in what the paper did not say. The Freudian analysts emphasized that their theories were constantly verified by their 'clinical observations'. As for Adler, I was much impressed by a personal experience. Once, in 1919, I reported to him a case which to me did not seem particularly Adlerian, but which he found no difficulty in analysing in terms of his theory of inferiority feelings, although he had not even seen the child. Slightly shocked, I asked him how he could be so sure. 'Because of my thousandfold experience,' he replied; whereupon I could not help saying: 'And with this new case, I suppose, your experience has become thousand-and-one- fold.'
Falsifiability is a criterion for the demarcation of epistemic claims such as hypotheses, as opposed to pseudo-scientific claims which may be based upon observation or observationally verifiable, yet not falsifiable, e.g. "he looks unhappy" or "a giant white gorilla lives in the Himalayas". The problem with induction is logical, as in what kind of inferences may be drawn justifiably from falsifiable statements.