Not in the usual sense, no. But his current state of communication problems would certainly be a "learning disability" in a typical school environment where things tend to be a bit faster paced, and teachers and students are often not as patient as people are with Mr. Hawking today.

A learning disability is NOT just "a disability which affects learning"

It's a specific thing. You're stretching the definition.

It's like someone says, "I don't have cancer, I have aids," and you reply, "Well, aids is a kind of cancer, since it gets into your body and then spreads like a cancer eventually killing you."