It doesn't, he had like 4.6 million shares before the ipo. The 500,000 number sold is just his class A shares. He'll still have 4.1 million shares of class b stock after this it looks like. The class b stock has ten votes compared to one vote for class a stock for any shareholder votes I believe. So selling only his class a shares won't change the percent voting control of the company he has by much. The person you're replying to is confused about how many total shares he has. I don't think the class b shares are being openly traded though, I think the ipo is just offering class a shares, which is what's causing the confusion here. He sold almost all of his class a shares, but still has plenty of class b.

https://www.sec.gov/Archives/edgar/data/1713445/000162828024011448/reddit-sx1a2.htm#i1b9a579e78a34dfa99f7f26daeec195b_100