He likely meant roleblocked. At this point, I'm not sure who to believe. I wouldn't put it past Assassin to claim Cop early day 2 under minimal pressure. I also wouldn't put it past Nemesis to have mafia no-kill in order to make it seem like a mafia roleblocker is town.

That said, there was nothing in the flavor about a roleblocked kill so this lends some credibility to Assassin's claim.

I do however think that Nem would target someone else--such as What--then Assassin. Then again, he could just be targeting him to lend credibility to his action.