"an informant apparently testified to this and a judge approved it" sounds very far away from what I understand "swatting" to mean normally.

AFAIK we have no idea if an informant testified to it, or even if there was an informant. Cops claimed that someone had told them about it, and the judge signed the warrant.

Swatting is the action or practice of making a hoax call in an attempt to bring about the dispatch of a large number of armed police officers to a particular address"

Either there was an informant, and the false claim was made to a police officer, or there was not informant, and the cop made a false claim to the judge. Either way, the intent was to get cops to show up and screw with Afroman, and that goal was achieved.