Don't you think it's possible that they, by chance, rely on both sight and scent to hunt? Just imagine what it would be like to have the eyes of a snake though- they typically only see from the sides of their heads as their eyes don't point forward much (although there are exceptions, as many arboreal species are) which would effect their depth perception and focus, not to mention how small those eyeballs are. Snakes, like a lot of predators (and human males, apparently) have eyesight that's quite sensitive to movement. According to that study I posted, they can also pick up details. Just only as they would see it.
Your pinky, having the smell of a mouse, was likely seen as, coincidentally, a mouse pinky. (lol) Odds are, he probably didn't notice it as attached to your hand, or not having any other rodent like features.