Bruckner & Bearman are studying abstinence pledges, which are specifically heterocentric and focus on PiV intercourse (through language about "Biblical marriage relationships and the like) as the crux of their definition of "abstinence," so, yeah.

It is however quite true that one of the problems that continually plagues the whole "abstinence" movement is that they never -- apparently for fear of saying too much by doing so -- articulate precisely what the dimensions of "abstinence" are supposed to be and the entirety of what it is supposed to entail... leads to all sorts of interesting casuistry & weirdness, as you point out.