You can shift responsibility for that knowledge wherever you want but I would say that at the age between 16 and 19 (which google tells me is the average age for AP classes) I would expect that knowledge from someone applying for AP credit. And if someone didn't know what the accepted file types (as stated in the FAQ) meant at that age I'd expect them to figure it out for themselves.

It's certainly not a well engineered user experience. Passing a physics test should require physics knowledge, not knowledge of image formats. I think understanding of image formats is actually fairly obscure outside of technical circles.

Maybe university IT departments are staffed by people. Maybe even at the college board it's just some IT guys trying to keep a shitty platform working. Maybe they did the best they could working within their constraints and they expected the same from students who have a vested interest in getting their results submitted. Maybe this is just much ado about nothing.