For those asking about the shotgun, the way weapons are mostly seen in a mexican historical context, is more based in a "we will defend our country against anyone threatening our freedom" than "I'm going to fuck your shit because the constitution allows me to buy a Barret sniper rifle".
Every school has a Revolución Mexicana event and kids are dressed like the peasants who revolted against Porfirio Díaz and they get to carry fake rifles made of wood (that look like a toy). Like any historic event, it's not always black or white when it comes to it, but the context of guns and firearms is quite a lot different than "hell yeah I bought a shotgun from fucking Walmart". And sure is a lot different than the "narcos are cool as fuck when they have their weapons in the open".
Thanks to the fellow user who posted the Adelita reference, I was going for a more general sense of the "why is there a shotgun in there".