The difference is, “who pays”?
A valid public protest will have no single ‘victim’. Nadav ‘protest’ targeted a single entity.
You understand men will ‘protest’ their ex-girlfriends for perceived wrongs, and that’s rightly called ‘harassment’, because it is targeted at a single person?
In contrast when Gandhi “stole” from the government by making salt, or people blocked the street to protest the Vietnam War, it’s not really a crime, because no single person gets hurt.
But if someone makes paper from trees in my forest, or blocks the entrance to my home, it is not a valid means of protest, rather it’s just harassment. They are imposing a cost on me.
And by targeting flyers only onto the offices of Bitmain, he crossed that line, gave them a cost. If he flyered the neighborhood, totally different.
Nobody likes to clean up a mess, and it is nobody's place to tell another how valuable his or her time is. If a Bitmain employee is worth $1000/hour, you cost them hundreds of dollars of cleanup. Who knows, the employee might be more valuable than that.
Not to mention their reputation. Now neighbors who know nothing of bitcoin will wonder what the problem is with Bitmain (and by extension bitcoin, which is bad for all of us).
If Nadav offered to clean up his mess, (or pay for cleanup) then it might make his actions more socially acceptable. But he didn’t. He proudly posted videos of himself, and deflected culpability.