Many Guardsmen had already made themselves obnoxious to both the RAs and the USs (for those who don't speak the language RJB and i are using, RA means Regular Army and refers to those who enlisted, while US refers to the United States Army, and means those who were drafted). For example, a trainee platoon leader in my basic training company had, several months earlier, said that if he, a Guardsman from Cleveland, saw any of "you hippies" on the street, he'd shoot us. There was by then already a good deal of animosity between the ANG and the RA and US soldiers.
I don't know, of course, what had happened to that guy in the tank motor pool, but i suspect he had said the wrong thing to the wrong person or persons, and got his ass whipped. We (not i or my friends, at least) didn't hunt up Guardsmen to pick fights with them, but we were long past the point at which we would take any **** from them. The ones who were marched off to a separate barracks had already been sobered by the experience of just a part of a day, and we did not hear a peep out of any of them for the rest of the training cycle. A few months after that, some idiot Guardsman at Fort Sam was crowing to me about how we'd be going to Nam, and he'd be home in a couple of months. I pointed out that he'd be kissing officer and NCO ass for at least the next six years, and he took a swing at me. I ended up preventing the other guys in the barracks from beating the **** out of him then.
There was already an "us and them" attitude between the Guard and the RA before the shootings, which just worsened the circumstances. It's the kind of subtle situation that you don't expect fire-eating bullshit artists to understand, especially those who were not there.
None of this probably existed when you were in the army--i suspect it was a product of the student demonstrations and street riots which grew out of the anti-war movement. It was already well known then that guys didn't get into the Guard (who were never going to Vietnam--although some few, very few, did, the general perception among draft age guys was the Guard was a "safe haven) unless their daddies had some pull. To further put it into context, in November, 1969, Nixon announced the lottery, and the end of almost all deferments, other than skilled work in the defense industry. That first lottery swept up a lot of people who had already married, gotten a good job, completed their university education, or otherwise made their start in life. The training units i was in were often full of guys in their mid- or even late 20s. One guy in my basic training unit was already, at 25, a professor of chemistry--he was a positive threat to us all. I was spotting for him at the rifle range one day, and explained to him that he had to jack the slide to chamber a round. The weapon jammed, and i could see the end of his cleaning rod in the barrel just in front of the chamber. I never did the low crawl so fast or so perfectly in my life. They were obviously not very happy about the situation, and the increasingly hostile and mouthy Guardsmen didn't help. After Kent State, most (but not all) Guardsmen learned to keep their mouths shut, to keep their heads down, and to do their time and get out.