I am not sure how else to possibly understandthan to be complaining about the use of Twitter AND SPECIFICALLY HIS/HER ASKING PEOPLE TO IDENTIFY PUBLICLY ON TWITTER.
My recollection is that the original tweet also had a video of the accused person at a different protest.
The tweet had 2 different pics from 1/6, no videos. Shockingly, the post that seems to have first mistakenly identified him is actually still up on twitter.
The reason why publicly ID'in (say, on twitter) is bad - aside from the potential of ID'ing the wrong person - is because literally the only reason to do that instead of just sending the info to the FBI is because you want people to see what a good sleuth you are. And that's just pathetic. I will say that I've seen a lot of good collaboration with these things on twitter/reddit/etc, but make you group of co-sleuths or whatever and take it somewhere private, and share your results with law enforcement, not with the twitter mob.