Not sure what it is. Usually when that kind of thing happens it is dry cracked skin on the feet that causes bleeding and it gets flung around. The fact it it could be a number of things. Does the blood on the toy look like it got there from spattering or does it look like it was from chewing?
If it is coming from the anus or intestine you'll probably see it smeared in with feces on the floor. Definitely check his feet, clean all the blood out of the cage so it's obvious if there is more blood. Make sure they both are acting okay and if it happens again anytime soon I'd see a vet. If it's in the feces it could be serious. If it's in the mouth or drooling out the of the mouth that can also be serious. Small skin nicks or cracked skin is not serious.
If the feet are cracked you may need to explore the causes of that and treat it to prevent infection.