You never had any per
rectal bleeding so far. It has been noted only after the anal
masturbation.
It is most likely to be due to some minor scratching on the anal
mucous membrane. It is a very delicate tissue. How so ever you are gentle, during masturbation, in the heat, you unknowingly become rather harsh. So the chance of this mucous membrane getting hurt is very high.
The other possibility is hurting the blood vessels responsible for piles bleeding hurt. But this seems to be very remote as the bleeding after that will be considerate.
I do not think there is any issue to get worried about the little staining. Keep a watch for some more days to see whether you bleed even without inserting anything in the anus. If you bleed, then you have to take surgeon's opinion.
However, I would like to alert you about couple of things:
1. Please do not insert the same toothbrush that you have inserted in the anus again into the mouth. It may carry very dangerous bacteria.
2. Instead of using articles like toothbrush, better to use dildo.