Wordorigins.org

The use of hot to mean excellent or fashionable dates to the mid-19th century. From H.W. Shaw’s 1866 Josh Billings, Hiz Sayings:

I dropt tu sleep, az a snoflake dus on the buzzum ov a silvery Lake, (i have a faint idee that this laste sentense, for lovlaness, kant be beat, handy.) I dreamed a good-sized, hot dream.¹