They did not ask him to leave, and he refused. They counted down the seconds he had the floor, and ordered his arrest the moment he went over the allotted time.
I don't know if you've ever been to a Town Hall before, but this is absolutely ridiculous. When you go over your time, you can either ask for more time or be told that you are done.
You shouldn't be arrested unless you intentionally refuse to conclude your time, or if you create a disruption. He did neither.
They arrested him because they didn't like what he had to say, and they want to send a harsh message to anyone else who dares speak out against Datacenters.
This is an egregious violation of First Amendment rights.