But then why is there now this warning above the BC.game thread exactly after the moment Cointrader supported my flag?
It looks extremely likely his support did the job.
It shouldn't be, as you can see, with only supports from Coin_trader and me [this screenshot was taken before post above, before Get-Paid.com supported then withdrawn the support, and thus, return the situation back to the same state as earlier today] the flag shown as insufficient. I take a look into their profile in guest mode as well and no, there isn't any warning flag against them. Unless you're referring to that negative score on their profile, that now shows +3/=1/-1?

I am no expert in how flags/trust etc. works, so I trust your judgement. But I do still see this message above the BC.game thread, even when logged out: Warning: One or more bitcointalk.org users have reported that they strongly believe that the creator of this topic is a scammer. (Check their trust page to see the detailed trust ratings.) While the bitcointalk.org administration does not verify such claims, you should proceed with extreme caution.