That big guy in red shirt, who looks like a friend of mine from down that way (further south and east though), has a pretty nice looking M-1 Carbine, complete with bayonet lug and everything. Gee, I though military weapons were illegal for individuals to own in Mexico.... Oh wait, criminals and political thugs don't care. (By the description, these are probably PRI-ista thugs, who probably would have peed their pantalones if a few pimply faced draftees with H&K assault rifles (5.56 NATO) had showed up. Better yet, a less "well equipped" unit with H&K battle rifles (7.62 NATO). I know those kids made me nervous when I was down there about 10 years ago). 
Given halfway decent first and a decent, not even good, hospital, no one should have died of a wound like that. Clearly no one knew what that aid might consist of, cause there's no evidence it was provided.
On the wound, I think you are probably right. The report I read said he died of a "stomach wound" which should not have been fatal. The
Mark in Mexico Blog site showed pictures of an ambulance that was in fact nearby but no one seemed to bother to use it until it was too late. And Mark also says that almost as soon as this guy went down someone stripped him of his pants and fled with them, it was not done for medical reasons.
Other reporting I have read verifies that those men were in fact Priistas, but what I think is particularly important here is that they were also public officials. They guys in the brown coat and red buttoned-up shirt were both elected in fact. No; they're not angels by a long shot. But as I have posted elsewhere, APPO was seizing private businesses and trashing them starting last Friday, and an assault on private property is supposed to invoke a reaction of the police, in Mexico and everywhere else but Cuba and Venezuela.