He's seen this sort of thing before. Of course Bigby has. If he hasn't seen it in the mirror before - too many times, really - then he's seen it on other people. That desperation to keep on fighting, even though it's clearly already over for you. Bigby may not be medically inclined enough to be able to tell everything that's wrong with Jason just from a quick look at the other, but it's clear that Jason is likely one or two more injuries away from ending up like the two men already currently on the ground.

It makes it relatively easy for Bigby to manage to drag the other guy along. If Jason shakes off the hold of his arm, then Bigby just instead grabs the other guy by the back of his collar, dragging him along like a mother cat would with a particularly naughty kitten.

That's priority #1. Edward and the stranger seemed out cold, but Bigby still wants to get Jason away from that spot just in case they're not. So he doesn't say more at first, just dragging Jason along through the snow until they're at least far away enough from the scene to no longer be within sight or earshot.

"Fuck, man," Bigby then finally says. His eyes still haven't returned to the way they were before, last time they met. They're still weirdly dark yet glowing. "What the hell even happened?"