Wrongdoing, I guess?

There are two components, really: legal guilt and moral guilt. Legally, he definitely purchased and transported a firearm illegally, and then shot three people with said illegally-purchased firearm. Morally, you generally don’t bring a rifle somewhere unless you expect you may have to use it, and you don’t bring a rifle to a riot unless you expect you may have to use it against rioters.

In the best case, he grossly underestimated the probability that he would have to use it, which turned the small net benefit of his presence as a “medic” into a major detriment in that two people are now dead. He also failed to recognize that possessing, brandishing, and using a firearm at a riot would directly lead to being attacked (in 2 of the 3 shootings, IIRC). It should have been obvious that an angry crowd wouldn’t have all the facts, yet would know that the person who just fired an AR-15 is dangerous and attempt to subdue them.

In the worst case, he went there specifically because of the possibility he would get to shoot people, rather than in spite of the possibility. The fact that he went without his parents’ permission—which hopefully wouldn’t have been granted—, as well as that he brought an illegally-obtained firearm, lends credence to this argument. IIRC, the prosecutors were unable to produce evidence that this was his intention, but the possibility can never truly be ruled out, and his publicity and associations following the trial suggest hey may have possessed malicious intent. After all, for someone who supposedly didn’t want to see BLM protestors dead, he sure works for/with a lot of people who basically do.