I encountered this type of marketing years ago and many are still doing its subtle marketing part of it is content marketing where instead of direct advertising they create a storyline that is relevant to what the audience wants to read of course they mention the platform they are promoting in their storyline.
You are right you have to be innovative to do this and you need engagement, some forums accept this, and some forums don't allow this, and some forums encourage this as long as there are no links in the post.
But it's hard to consider this spam as the content does not revolve around the mentioned product but around the storyline.
But if you checked recent post history of user mentioned by OP, you'll find out that they frequently mention word "bitget" on majority of their post. So it's not subtle marketing and IMO should be considered as spam.
This is why I posted some forums that accept this some forums don't allow this and some forums encourage this as long as there are no links in the post.
When I still had my forum we had some members who created a discussion about current events and they managed to mention the name of the product in a subtle way focusing on the storyline, we sometimes deleted the part that mentioned the service and retained the discussion.
It's really up to the moderators they have full discretion on this as they are guided on what action to take.