Maybe she smelled of rodent ??
Sorry, but there is no knowing what goes on in those tiny heads, but I can understand your shock. Its kind of embarrassing when that happens, esp. to friends and family whom we are trying to show how "cool" our snakes are...
Never heard of one biting to "hold on". Technically that would work I guess, but I'm more inclined to think some smell or heat or a combination of it triggered his feeding response...