Probably club spamming. You could originally post like 100 notes in club easily in 10 seconds by clicking the post button a bunch before it actually posted but chess.com thankfully updated that.
I honestly find it unamusing to spam and disturbing to others so I never do it. XD
Not even when others allow it, I just don't.
Back when there were lists of top point getters, there were some people with hundreds of thousands of points. I could never figure out how they had done it.