Like I said, I don't know the whole story, relationship of the kid to the other student or if the kid himself was known for causing problems. As a stand-alone incident, it's still a tough call. Yes, school is important but even more important is following rules.
I just don't know enough to make a true judgment call. I don't think they are 'hiding' behind the warnings. Warnings are exactly that, letting you know that a punishment IS coming if certain behavior continues.
I'm usually the first one to yell "zero tolerance sucks!" but this doesn't strike me as a typical case. There was way above 'zero' tolerance for the behavior and every other student seemed to comply, this one didn't.
Context? I mean, I can't imagine a teacher doing that unless he was told repeatedly to stop doing something. Our kid got a reprimand for "not standing in line properly". Come to find out he was moving around, moving others, and trying to stand next to his friend when there was a set order (for something, don't remember). But I could easily phrase it to "Our child was standing in line next to his friend and got a reprimand".
Also, some teachers will just not like your kid. So things they do will annoy them more. Is it right? Nope. But it will happen. Our's second grade teacher did not like him at all. Letters home all the time, we felt like we had 'that kid'. Come 3rd grade his piano teacher loves him, he does great with his teacher, and his after school care thinks highly of him ... so YMMV when it comes to teachers ... just like ANYTHING in life where it's left up to a personal judgment.