[ludwik]

20 million unique users is not that much. I don't understand the claim that this constitutes 9% of all IP addresses. It doesn't. There are about 4 billion public IPv4 address. 9% of that would be closer to 300 million.

[nicomt]

You're right, like others said in the comments the 9% in the comments is from total active hosts tracked by Censys (~231 million). But I still think it's challenging to have that much reach and unlikely to be an ad campaign. Using numbers from the website bellow the cost of getting 20 million impressions would be around $43,200 on the low-end for YouTube ads and can be much higher on different platforms. That is also assuming perfect efficiency were you we have exactly one impression per IP which is unlikely to be the case.

https://www.guptamedia.com/social-media-ads-cost