Why wouldn't he consider that Winry would go after him if he suddenly disappeared and showed up next to the ring? It's clear both of the twins are fighters, and they think he's weak. If they see him in danger, of course they'll get involved. He's been pretending to be weak all this time, but when something like this happens, he ignores his own efforts and goes straight up, endangering everyone around him who will naturally think they have to protect him.