No you are right; I just grabbed a piece of spectra off my climbing harness. After citting a piece I took out the spectra core and melted it with a lighter.
I think I associated the fact that the hot knife at the store could never make a cut; we always used a FRESH razor blade to make a clean cut. Then we melted the sheath by itself.
Turns out it does melt it just melts very differently than the sheath material which is regular perlon.

A lot of climbers refer to all varieties of specialty cord wrongly as spectra. But that website turned out to be wrong on more than one thing.