Starting in 'media res' - in the middle of things is a literary technique which subverts the idea that a story should have a beginning, it also invokes the feeling that we are in the middle of things without knowing what is going on, and we must spend effort to discover this, that is establish coherence.
The absurd is one reaction when the world loses meaning. There is a well-known theatre of the absurd which takes off from Camus work.
As you point out, Camus work is over 60 years old; to get a grasp of what he is saying one has to immerse oneself or at least have a nodding acquaintance of the intellectual currents and preoccupations of that time. And one of those themes is taking the Nietszchean 'Death of God' seriously by the intellectual elite - which probably given serious impetus after two devastating world wars (which was also what propelled the absurdism of the dadaist avant-garde art group). What could be more absurd than the trench warfare of the first world war, the use of men as cannon-fodder? Of course this intellectual climate is normative now (I don't mean absurdism here but athiesm).