Just because ringworm is highly contagious doesn't mean that every mammal in contact will get it. We see dogs or cats in a single household where only one will contract ringworm and show signs while no one else ever gets it.

I personally have handled animals with ringworm(I didn't know they had it before, obviously, *skin crawls*) and not gotten ringworm, neither have many owners of cats that handle their cats daily, with the cat having diagnosed ringworm. So it's not a given that all the rats would have ringworm. Additionally, the other rats may not have been showing any signs of ringworm YET, and then shown the ringworm later, but since the OP was banned, we never heard, or he never bothered to post the info. There's no telling.