For what it’s worth, the guy who mostly maintains the Wikipedia page agrees with you. And yet even so, at least for now, the Wikipedia page states “The majority of fediverse platforms … create connections between servers using the ActivityPub protocol” – which pretty clearly implies that not all fediverse platforms use the ActivityPub protocol.

Anyhow whether or not you agree to disagree … we disagree. Time will tell how broad usage of the term evolves. In the original article I pointed to examples of TechCrunch and Mike Masnick using the term in the broader sense, but maybe those will turn out to be points off the curve. We shall see!