I am from Galicia and shot #3 is definitely not representative from Galician Carnival. Galicia is a gorgeous destination, especially during Summer, but don't expect to have the kind of fun that the guy in photo #3 is having :-) Here are a couple of videos that provide a much better representation of what Galicia currently is: https://www.youtube.com/watch?v=uG1hkCzefL0 and https://www.youtube.com/watch?v=ZtUqecPNXgI
You can definitely find popular festivals in Galicia where getting drunk is the main goal, if that's your thing. I'd say it's a waste of time, though, given how beautiful and great Galicia is. Better to get wasted closer to home.
When you have Magnum photographers go to a place, they are not looking for the ordinary in the ordinary, but the extraordinary in the ordinary to create a sort of juxta. It's a bit exaggerated, a bit voyeuristic, in a minor sense exploitative.
Therefore, many of these commissions will end up not with representative photographs (as one might get from vernacular snapshots) but with images which show the more unusual shots, or the ordinary framed to be poignant. That's what these people get paid for.
(Yeah, I know the "hidden" it's in the title itself and should warn about generalizing what's being shown, but still).