Ive delt with reptile mites before and that doesnt look like mites. I have to agree with the wood mite theory. Wood mites wont get on the snake but I do know from experience that some types of wood mites will bite a human. Eeek!

Plus reptile mites are generally round. If you can get a couple of those things out of there and look very closely you would see tiny legs like a round flea. That picture doesnt look like a bunch of uniformly shaped bugs and if it were bugs they would all look identical, just slightly different sizes.

I use that mulch for my little borneos right now and I have never had anything like that show up in the water. I must have just gotten lucky in that dept.

Keep an eye on it and let us know what you find out. Another place mites will be if they are on a snake is around its eyes and vent area. Its gotta be either wood mites or just specks of dirt/wood from the bedding.