privacy – Isn’t Youtube supposed to forget what I did during an incognito session?

I hope the question is applicable to this forum. If not, please, point me better Stack where I could ask it.

When I go into incognito session and then use Youtube, I always thought that it’s like coming to the site as a totally new person. How surprising it was when one day I watched a cabaret (not a very trendy, nor fashionable thing to watch) in incognito mode and a day later, on the same browser, on the same computer, in incognito mode I received a recommendation for me to watch the same cabaret, on the main page. I wasn’t logged in. Neither am I logged in on YT in non-incognito session, but there I didn’t receive any cabaret recommendation, so YT treats these two sessions as different users and give different recommendations.

I could think that YT knows something about my net, so they could basically recommend me anything that I watch on any computer in the range of the same wifi net, on any device, but YT doesn’t do it.

So how did Youtube know that I had watched a cabaret a day before and that I was in incognito mode too? How does it all work? I reckon he wouldn’t know if I had used a different browser?