why

We use the term "special" to describe people who are mentally deficient, because it is "politically correct" to do so. Other terms tend to be derogatory and hurtful stereotypes.

It's a kind, non mean way to say things.

Most likely it is used as an accepted way of describing a disability. The words are positive sounding, non-offensive - if you will. And the type of accomdations needed for this person are special in that they are often different than the norm. So special is a much better way of saying this person has needs and they are as follows. It's a way of communicating a certain message without using words with a negative image.