It is indeed both: confirmation bias and survivorship bias. At least it can be interpreted this way.
Adding to this it is mainly circular reasoning based on confirmation bias:
the tendency to search for, interpret, favor, and recall information in a way that confirms one's preexisting beliefs or hypotheses. It is a type of cognitive bias and a systematic error of inductive reasoning. People display this bias when they gather or remember information selectively, or when they interpret it in a biased way. The effect is stronger for emotionally charged issues and for deeply entrenched beliefs. Confirmation bias is a variation of the more general tendency of apophenia.
But because Andy is special with special needs it is also a form of attentional bias:
The tendency of our perception to be affected by our recurring thoughts.
Why is Andy special? Not so much because of his obsessive gay-daring. Presumably, because he likely has "the tendency to see oneself as less biased than other people, or to be able to identify more cognitive biases in others than in oneself. Therefore he does not see a need for some other method than
The tendency to test hypotheses exclusively through direct testing, instead of testing possible alternative hypotheses. (Congruence bias)
Even after being pointed out to him that his reasoning isn't sound he will suffer the continued influence effect:
The tendency to believe previously learned misinformation even after it has been corrected. Misinformation can still influence inferences one generates after a correction has occurred.
That is because he is a conservative with accordingly
The tendency to revise one's belief insufficiently when presented with new evidence.
People in this group are susceptible to the ultimate attribution error:
Similar to the fundamental attribution error, in this error a person is likely to make an internal attribution to an entire group instead of the individuals within the group.
But this can be excused to a certain extent by proto-/stereotyping and bizarreness effect:
Bizarre material is better remembered than common material.
All hope is not lost for this kind of conservatism high though, mere exposure effect to the rescue:
The tendency to express undue liking for things merely because of familiarity with them
This list is not exhaustive.
The best fitting category is the result of your frame of analysis:
is it about Andy's behaviour, attitudes, information seeking, -processing, -interpretation? Real world data, base rate?
It depends on your focus to analyse this case. Based on the information given, both of your assumptive categories seem applicable. But there are more.