He could have surrendered when it was clear that the pack was done for.
It's up to the GM whether to accept a surrender - either way, the pack didn't surrender (all the wolves need to surrender for it to even be considered as valid). I am staunchly against surrender as a game mechanic in general, so I for instance disallow surrenders in my games. I think GMs should be upfront at the beginning as to whether surrenders are accepted or not.