is there a reason all the steam guides and youtube gameplay videos show different cutscenes, characters appearances and even weapons and settings versus what we're actually playing in the game?

i first noticed this in the first level. i was missing a piece of treature and consulted one of the steam video guides; they all depict a segment where you have to plant some dynamite to blow up a fallen statue. this isn't in the game, but it's just the beginning.

anyone have any insight?