I can hardly call myself an expert on the "alt right" either, but the difference is in use of term.

When leftists think "Right wing" in the US think of the Christian theocracy. However, conservatism is only one sect of the right. The right is also reactionary, and the alt-right is definitely reactionary. I'd argue the alt-right fits nicely into Wikipedia's definition of far-right politics [1].

[1] https://en.wikipedia.org/wiki/Far-right_politics

Edited because my sarcastic use of tone didn't really have a place in the discussion.