CALLED IT! Normally these cuts would drip down the finger. Usually the entire hand doesn't get covered with blood unless you smear it.
Or close your hand into a fist, like the normal reaction that occurs when pain happens in your fingers or hand.
If he's then rummaging around for a camera or whanot, then his hand is going to be moving around.
If you do that, then the blood will drip down the hands. You can see where the blood in his picture flows down the natural creases of his hand.
Hamster teeth are incredibly loving sharp and powerful, especially when you give them things like wood or cardboard for them to gnaw on.
My old hamster bit through the metal bars of his cage. It took him time to do so, but he managed it.
Human skin is much weaker than metal.
A hamster can easily make a deep cut into skin. They also have curved teeth, like a rodent. This causes the cut to exist in a curve, which promotes bleeding and to some extent (if hamsters were much bigger, it'd be worse) prevents pressure being applied to stop to bleed.
It's not at all uncommon for a hamster bite to cause quite a painful and deep cut which can bleed quite profusely, even if you aren't haemophiliac.
