According to the OP (and the wikipedia article, of course there is one, perhaps you will find it a less shoehorning source on the event, I agree the article is a bit... boosterish), the boycott worked, and lowered the price of meat? Which seems to be a major problem with your argument that it made no sense as a political tactic and couldn't possibly work... it did work?
The wikipedia article provides a bit better context, that it also involved a battle between butchers/retailers and the meat wholesalers who provided the meat ("the meat trusts", which is a great phrase).
> On May 11, 1902, around 400 kosher butchers on the East Side of New York organized a boycott of the meat trusts to put pressure on them to lower the cost of meat. However, the trusts were too powerful and the butchers ended their boycott. In response to those unsuccessful attempts, the women of the Lower East Side Jewish community, led by Fanny Levy and Sarah Edelson, held a massive protest.[9] On May 15, 20,000 protesters, mostly women, took to the streets to attack the butcher shops.[10] They smashed shop windows, poured gasoline on the meat, lit it on fire and threw pieces of meat at police officers. By the end of the day, 85 people had been arrested, 75% of them women
OK, honestly I have a lot more questions afterreading the wikipedia article. This is an even somewhat stranger event than the OP suggested... the butcher shops wanted lower prices too, but the women rioters smashed the butcher shops... and then it worked, the butcher shops said, great, we're joining the boycott too and not selling the meat until the wholesalers drop their prices... and restaurants joined the boycott too... and eventually the wholesalers lowered their prices, and the butchers passed on the price drop.
Oh, and as far as "not many" butchers, note that mention of 400 kosher butchers on the east side of manhattan? I don't know how many butchers there were total in manhattan at the time, but 400 butchers is a lot of butchers.
I'm also really loving the image of women throwing burning hunks of gasoline-soaked looted meat at police officers as a weapon. That one paragraph from the wikipedia article has so much to offer.
Still seems like a weird thing to do.
Wikipedia is rife with nonsense sometimes.
But yeah, unfortunately the wikipedia source for the burning meat projectile claim is to a web page that makes the same claim without really citing it's source (beyond the name of a historian). We'd have to do some research to see if we could find a cited primary source that this claim came from originally, and how it appeared there.
I really like the image regardless. It does not seem implausible to me, generally, with kerosene. But it's an enjoyable image either way.