The books and comics are canon but halo legends most certainly was not.
Well thats cool, there is still a bunch of games with silly shit in it , and spartans acting chummy and jovial. Like that entire video game... staring.. spartans acting chummy and jovial... until the end.
My point is, spartans acting chummy and bro-ey isn't uncommon... at all. They are just really dudes in suits ( yes I know its more complicated than that ) and MC seems to be one of the weirder more silent ones. So i dunno a bunch of dudes getting hyped they are winning a training simulation after the reinstatement of the spartan program seems... normal. Seems like a subplot that i would not bat an eye at.
I don't think that gif out of the ordinary for the silliness levels in halo.