If it randomly mentions other users, and if it comes in such masses that Mastodon admins have to raise the shields and Fediblock the hell out of dozens of instances, then it’s spam all right.
That said, the last spam wave was organised on Misskey again, but carried out by bots from Mastodon instances largely abandoned by their admins. At least partially, this was the case for the first big spam wave as well.
Good to know.
Strangely, people don’t seem to mind.
I guess then a key difference is that Bluesky is presented to 𝕏 users as the same kind of monolith as 𝕏 whereas Mastodon is presented to them as a huge number of instances from which they absolutely have to pick one.