It's still relevant. There are still numbers lower than 1%. Less than 1% of viewers will upvote/downvote a video they watched, which is much easier (and less expensive) than paying.
About 1% of the people shown an ad (or any content) will even consciously acknowledge it, while approximately 1-3% of the remaining 1% will interact with it, and then 1-5% of that remaining group will actually buy the product. The 99% who didn't acknowledge its existence in the first place don't actually factor into anything other than how much you get charged for the ad.
The difference between the article and the OP's scenario, is that the OP already filtered the 99% and converted the rest. Now there is only one conversion left, which is to make them into paying customers, which is a much higher rate than 1% when you already have a captive audience.