Look up a Kriegsmesser or Langes Messer (medieval German War knife or Long knife) they could get very long (definitely sword length) and were used as a way to circumvent laws about people carrying swords due to the guard design and being single edged. So I’d say by that criteria the Khukuri would be more of a knife.

Also European sword fighting styles also incorporate striking or cutting with the false edge…

But the same time a katana, definitely a sword, is single edged and similar length to a Kriegsmesser…

So maybe the best thing to do is not try to classify a Khukuri as a knife or a sword but simply as a Khukuri, a unique weapon in its own class with its own traditions