Site A and B have to collude in order to make that inference. Outside of Cloudflare, no one is colluding at that level.
replyPlenty of people own more than one website. You're also forgetting about random site assets like web fonts, CSS, JavaScript CDNs, etc. etc.
replyThat would only be true if there were no ad networks.
replyBut today’s internet is essentially a giant ad network.