He never had a noble goal, so no, he isn't one.

There is some slight ambiguity to some of his actions, plus his tragic backstory, and the fact that all of his worst actions were under the Mind Flayer’s influence.

That would make him a scapegoat/possessed or brainwashed villain. Anti-villain's have noble goals. Billy does not.

“However, Anti-Villains do not necesarily have to have noble goals, as some can simply meet all the other criteria”

He does check off most other criteria (sympathetic motives, insecurities, not super heinous, and redemption at the end).

He's tragic but he sure isn't an anti-villain. Anti-villains have a noble goal that they go too far to achieve. Billy never had a noble cause he was fighting for