When you see the two words Deaf and deaf you may just assume that on this particular day the author decided to use a capital letter instead or a lower case letter. But in fact this small changes makes a slight difference in the two.
deaf- means simply unable to hear.
Deaf- is an identification. It is a culture. It is a type of person.
For example: A person can be Asian, White, Indian , Black or Deaf, with a capitalized D.