Is this stray cat's bumpy skin and closed eyes due to mange?

It does look like Mu has mange and even possibly a severe ringworm fungal skin infection as well. The eyes being semi-closed may be due to the mange/ringworm infection of the eyelids causing swelling/discomfort or he may also have an eye infection/conjunctivitis as well. Topical monthly flea products for cats called Revolution or Paradyne are often effective against sarcoptic mange and would be easy enough to apply to Mu. Ringworm lesions are usually circular areas of hairloss but can progress to covering large stretches of skin and look similar to how Mu looks in the pictures. Both diseases can be transmissible to humans and Mu is likely not rabies vaccinated so I would recommend avoiding handling/touching him without heavy gloves. If you are able to bring him to a local veterinarian or shelter, they may be able to provide Revolution, vaccinate him against rabies, provide a topical ophthalmic antibiotic ointment if indicated and look more closely in his mouth, as well as perform diagnostics to rule out a severe ringworm infection. Good luck!