So, does oral sex qualify as sex?
I had to chuckle when I first read the question because, for me, if it has sex as part of it's name, then yes, oral sex is sex. It's like asking "is the hot tea, tea?"
Well, no. That's not the way language works. If I invite you in for a "cup of tea", you'll be rather surprised if I pour a small dollop of Lipton's iced. "Tea" means different things in different contexts, and while we would admit iced tea to be a "type of tea", it would not be what we would consider to be "tea" given the very particular confines of the question. (Wittgenstein uses a better example: "teach the children a game" being taken to include blackjack. It's gaming! Right in the name!)
And so it is with sex. I would simultaneously say the oral sex is a form of sex, and not feel strange saying "I have only had sex with [X] number of people", where X includes only those I've had intercourse with (but not just oral sex). That's because, like with tea, certain types of questions imply a sort of shorthand that is understand by all. We can participate in that shorthand without actually excluding the other elements of the object. And insofar as we understand intercourse as a fundamentally different type of sexual expression compared to oral sex, this sort of understood distinction makes sense.
The author also claims that sex-as-intercourse is "heterocentric and phallocentric". The former is a stronger claim. To the latter: intercourse does not have to operate within rhetorical confines that cast men as active and women as passive. We can use words like "penetrate" or "pierce", sure, but we can also talk of "consume", "devour", or "envelope". Or (horrors upon horrors) we can use both. I think it's a dangerous game when we ossify heterosexual sex as inherently male-dominated, rather than seeing that domination as a product of particular patriarchal assumptions that can be contested.
As to the heteronormativity, I think this goes back to my point about meaning and context. If I ask a gay or lesbian friend (presumably after a few drinks) "how many people have you had sex with", we both understand that here the context is not restricted to PIV intercourse.
Humans are flexible creatures. We can handle this sort of ambiguity.