Biden is the Democratic nominee. Sure it’s not official until August 19-22 but unless he resigns, dies, or is otherwise fully incapacitated before then, he is the candidate who will be on the ballots in November. None of those possibilities seem likely.
It certainly doesn’t always get it right - I’ve seen subjects lit by bright sunlight in a nighttime background, or just from a wildly different direction, but within a subject the lighting usually seems consistent.
I’ve wondered the same thing myself, my assumption is that it just correlates how lighting works across millions of training images, much like how it manages to get gravity right most of the time.
Maybe he did aim for the center…