Having done a quick search it seems that some people here have suggested that he's Alpha NT, but based on his quotes (these and others I've read) and theories, I think he's LIE. Te + Ni > Ti + Ne.
But it is impossible for a LIE to be absent minded. A LIE can never exhibit the traits that are attributed to Smith, so he can't be a LIE. He must be a leading intuitive type.