I imagne that is a large part of the issue, but the article begins with someone who noticed a difference in his own experiences, following a candidate triggerin

I imagne that is a large part of the issue, but the article begins with someone who noticed a difference in his own experiences, following a candidate triggering event (an unspecified minor surgical procedure.) This is not proof of anything, but it suggests that in some cases, there is something to the idea beyond just mis-communication. In this case, there is also the physical evidence from brain scanning. I would guess that some proportion of those self-reporting as aphantasic would be indistinguishable from the general population by such measures.