Interesting perspective, but changing the definitions of sexual to only those encounters where the pairing of gametes is possible is just a bunch of linguistic gymnastics. I suppose by your definition that anyone who has had a vasectomy doesn’t have sex anymore but just exchanges bodily fluids since there are no gametes in the transmission.
He hasn’t changed the definition. If anything he’s identified how lazy others have been in applying ‘sexual’ with any activity involving genitalia that doesn’t involve elimination.
Procreation is the VERY REASON for sex. There is no other biological reason for sex, at all. As such, everything else isn’t sex, but play, assault, or domination.