I've seen it used both ways on CPF. It seems to be used more frequently to refer to incans that have been modified to run hotter/brighter than stock, because the word "incan" suffices just fine to refer to the genre as a whole.
FiveMega captured it. It is akin to when customized higher performance Hot Rods were done with various cars. It's beyond a stock incan setup. Good to see member HotWire still burning brightly.
I would go so far as to say it's derived from the incan filament "wire" being over-driven to the point of being "hot" as in hot rod. Hot Rod - Hot Wire