I think to cater that is you may post a scam accusation first on the said account then link that to flag him.
You can create a flag using a link on a person's trust page.
I think that's a good find on you because if you have created a self mod accusation thread about him and link that to flag the account that will not still effect. I think you found a good bug, I don't know if this has been found already on the trust flag thread of theymos but I guess it was the first time I heard it. By the way, the trust flag system will celebrate its first anniversary by tomorrow.
You don't flag topic, you put flag on user that created that topic. I don't see a reason why you can't create flag against OP.
I think what he meant is the link to be linked on the flag.
Edit: By the way, @MagicByt3 don't double post, I see it below my post. Edit the first reply instead of creating another reply.