"If 97-98% of people are hetero, in what sense is that not a norm?"

It is the norm. You're just confusing "norm" with "normative."

Normative: prescriptive (seeking a certain standard)
Norm: descriptive (what is predominant in the status quo)

Definitely heteronormative, though:
"So why don't I warn against heterosexual experimentation too? Because
this isn't a two-way street; many females would reject a male for
having engaged in homosexual activity, but no gay men would reject one
for having experimented heterosexually. So it's rational for a male to
postpone homosexual experimentation until he's certain he's gay."