I think this is a nit. "split-phase" is two 120V legs 180 degrees out of phase with each other. The word "phase" is starting to look spelled wrong to me, right now. I don't see the fundamental difference between "two phases [...]" and what i said "not single-phase"

I understand wye and three-phase power, and i also understand that when we plug into a scared face outlet[0], that is a "single phase" - but the stuff delivered to our house is two phases of 120VAC, 180 degrees out of phase.

again, it's a nit. you can use two conductors on a three-phase system and get a single phase, as well.

[0] NEMA 5-15R

My comment was less a nit and more I didn't understand how it really worked! Thanks for correcting me.