sam: an interesting teshuva. First he calls a microwave ??? then he writes it is steam. in the end he quotes Reb
Moshe and makes your distinction to resolve his chiddush with Reb Moshe. In any event, Reb Moshes basis for his Psak did not play out and the Metzius is inaccurate.
BTW Shvus Yitzchok actually distinguishes between a microwave running on solar generated electricity which is ?????? ???? and a gas or coal burning generator which is ?????? ???