Hi,
Yes that is definitely naked flesh where the scales have been cut or torn off.
You need to keep his cage as clean as possible so I would probably change the newspaper to paper towel and take everything else out.
I really do think you need to take him to a vet to get a decision on anti-biotics to prevent infection and some cream to help with the wound healing. I can never remember the name of it but I think it might be silver sulphadine?
For future reference if you cut the hole from the rim down then turn the tubs upside down they are far less likely to injure the snake than a hole cut in the bottom or side as, if the snake is too big, it simply lifts off him.
And since that is an open wound I'd bite the bullet and pay the extra to see the vet sooner rather than later. Imagine having a chunk of skin torn off yourself.
dr del