I was also there. We (ie the people I interacted with) called myspace social media and considered discussion forums to be a specialized subset of social media.

We also considered myspace to be a social network (due to the friend graph) while forums were not.

The chans were a weird almost edge case. I think they qualify as social media but the lack of persistent identities significantly changes the dynamics (obviously).

Nobody called a phpBB forum “social media” 20-25 years ago.

Nobody.

Not only did we do it back then, scroll around this thread - it's still a thing today, people are calling HN "social media".

As far as I know chans are always considered "image boards" and they are usually distinct by the fact that the information is "pushed off" the board after a time or amount posted afterwards.

Image boards, which are a subset of forums, which are a subset of social media.