CanadaBob2 is correct on this one.  I have been horrified that DT (or anyone) would have mocked anyone, let alone a disabled person.  But, he is right; apparently DT has used this hand motion on many occasion in his mocking.

Now don't get me wrong, the mocking is wrong, full stop.  But I don't believe he intended to mock the gentleman because he was disabled.  Apparently it was a general all around mocking (which is just shameful in and of itself).