Since it's a made-up term about a make-believe sexual identity (asexuality), it doesn't really matter, but originally on the internet it basically meant someone who feels attraction to another person only after developing emotional/romantic feelings for them.
So it's a fancy word for people who want to feel special by propping up a common human experience as a ~sexuality~.
The person who first brought it up in this thread was using it incorrectly either way, even going be retarded asexy standards. DeMiSeXuAlS are still either hetero/bi/gay. It's not a stand-in for actual sexual orientation.