I strongly disagree, his comment is not an ad, it is content. We all came to this page looking for comments like that. Every single experience in life changes the way I think and feel, that doesn't mean everything is an ad, the defining characteristic of an ad is the fact that it is unwanted, that it is imposed on people as an attention tax imposed on some other experience we actually want.

Another difference not mentioned by sibling comments is that ads are purchased. They are necessarily the domain of the well-funded and therefore already-powerful, and whose purpose is to typically to enhance their purchasers wealth or power. They are a tool for inequality.

Not really. Comments are comments. Not ads. You came here to read the comments. Nobody paid some ad company to show it to you and force the ideas into your head. The fact you agreed with the comment doesn't mean it's an ad, it means you found it persuasive.

The difference is that his "ad" is relevant; you are on a comment thread about ads reading his (relevant) reply, similar to seeing an ad about a phone in a phone store.

In contrast, ads in most public places are completely irrelevant and unwelcome.