It was a taunt. It wasn't just a stare, he also deliberately stepped in the dude's direction too. To his credit, Giannis seemed to quickly realize that was a bad decision. But that was a taunt and absolutely could have started some shit (which is why taunting isn't permitted).
Now, I don't know what he got his first tech for. Wasn't watching. But I would also suggest that regardless, once you've got a tech you should probably not be doing stuff like this the rest of the game. But, I can also understand wanting the referees to use some more discretion about handing out second technicals.
Did Josh Allen's mom write this or something?