An outbreak like you describe takes months to build up to, so they probably came with them

I suggest every time you take a snake in to treat it as if it did have mites.
PAM is something every reptile owner should have a can of sitting on the shelf, glad you did the right thing and ordered up a can
Until the PAM comes I suggest just keeping the cage clean and them on newspaper/paper towels.

The water might have been recently swallowed, ball pythons will spit water out if you hold them right after they drink, so maybe??

Treat once a week for 3 weeks and the problem should be gone.
Treat the whole area lightly including the carpet if there is carpet.
What you are seeing is the results of eggs hatching numerous times creating all those little bugs.

Good luck!