I personally read that incident with the portrait as being linked to Envoy Jaime's quest, because I've always been on his quest when I first visit the Tawon. It honestly didn't occur to me that it might not be linked somehow. I don't know for sure either way.
If it turns out not to be linked to the Raptors' quest for Gryfyn, though, there is the possibility Lilith brought up. The MC's trainer does mention later in the game that they had been talking with rebel scouts. Given that, it's possible that either they mentioned the MC's description innocently and someone from one of the factions thought it'd be a good idea to off the MC, or that a party of rebel scouts spotted the MC after the first run-in with Ghorus, assumed he hadn't finished his job and decided to hire someone else for that job instead. (Incidentally, this would also help explain Konstina's reluctance to pay Ghorus what he considered his due.)