It started in D&D 2.0 for certain, might have been in 1.0 but I don’t remember. That predates Warcraft by a few months…
Also that’s the way it worked in 3.0 D&D. You had to cast “Cause [Intensity level] Wounds” to heal Undead. I dunno about 4th, but my friends that play 5th run it that way.