I agree, the "Does one type of damage but gets stab as if it's another type" defy the meaning of stab. I mentioned a while back that this would effectively be called DTAB which is stupid. Young players don't even know what stab means and to tell them that this is dual type attack will confuse them. Heck, except for rare circumstances, the game does not even acknowledge stab exist, what makes you guys think they will acknowledge dtab exist?
lol, you guys are struggling to make this complicated.
It's no more so than Psyshock, Psytrike or Foul Play.
Here is Psyshock's ingame description:
"The user materializes an odd psychic wave to attack the target. This attack does physical damage."
It's listed as a Special Attack so anyone with minimal knowledge of game mechanics will let pokemon with high SpA use it.
Here is a hypothetical Glow Punch description:
"The foe is punched with a flaming fist. This attack does Fighting type damage."
Simple. It'd be listed as a Fire attack so ahyone with knowledge of STAB would expect it to be boosted when used by Fire types.
The term 'dual typed moves' is not official as far as we know.
It was a description by the leaker of a gameplay mechanic that s/he saw.
Granted, I'm not saying that what's being here proposed is what it will be. It's just what I think.
OTOH, the suggestion that it would be this mindbending, terribly confusing thing doesn't compute.