He talk about something that might be of interest for these people.
It doesn't sound like he was spamming or doing anything annoying.
It sounds to me like a more human way of doing advertisement. The only difference is that he is actually there to have an actual conversation about it.
That's why youtuber put #ad on their videos
I don't know what they count as advertising per se but if endorsement via private message counts then the FTC's page[0] calls this out as "position with the company":
"Connections between an endorser and the company that are unclear or unexpected to a customer also must be disclosed, whether they have to do with a financial arrangement for a favorable endorsement, a position with the company, or stock ownership."
[0]: https://www.ftc.gov/tips-advice/business-center/guidance/adv...
From the FTC
>If you endorse a product through social media, your endorsement message should make it obvious when you have a relationship (“material connection”) with the brand. A “material connection” to the brand includes a personal, family, or employment relationship or a financial relationship – such as the brand paying you or giving you free or discounted products or services.
https://www.ftc.gov/system/files/documents/plain-language/10...
Ethical advertising is honest and up-front. If you need to be clandestine about it, you're doing something unethical pretty much by definition.