The reason this has taken hold is because of MSM articles drumming up interest for the Q documentary and alluding to him being behind it all. Most of these articles will reference the following exchange between Ron Watkins and the filmmaker Cullen Holback which is in the trailer itself.

“You’re going through a possible list of who Q might be?” - Ron “That’s right. You’re on the list." - Cullen “Well, let’s continue then.” - Ron

And then attempt to substantiate it further by using this VICE article:

https://www.vice.com/en/article/93wqm7/ron-watkins-meet-the-dangerous-qanon-figure-doing-whatever-it-takes-to-win-trumps-approval

The Ron / Q article is always modified in terms of headline, slight variations. But the body content is almost always the same...

SOURCES:

https://www.independent.co.uk/news/world/americas/us-politics/hbo-documentary-qanon-ron-watkins-b1818137.html

https://7news.com.au/technology/is-this-q-documentary-claims-ron-watkins-could-be-qanon-leader-c-2371337

https://www.news.com.au/world/north-america/leader-of-qanon-conspiracy-group-unmasked-new-documentary-claims/news-story/6eb7c3908595313fce6e070692f7eb5e

https://www.the-sun.com/news/2522119/qanon-leader-q-revealed-ex-8chan-administrator-ron-watkins/

EDIT: For extra reading, it would seem Variety has published a review of it already. I am providing the link for other people to view but I am not endorsing anything to do with the review.

https://variety.com/2021/tv/reviews/qanon-documentary-q-into-the-storm-review-1234930893/