did you look at the nice graphic representation? no, not every gun in the US is semiauto, there are plenty of revolvers, pump-action, break-action, and lever-action firearms. There are very very few privately-owned NFA-compliant, legal automatic firearms.
If it wasn't guns it'd be swords, if it wasn't swords it'd be pointy sticks... We're an intelligent social species that forms groups. Not much we can do about it any time soon. At least most places don't condone burning humans alive anymore.
Yeah I don' trust what Mexican authorities have to say as far as I can throw them, this goes for the UN as well.