A few days ago I opened a youtube video in chrome incognito mode so it won't pollute the feed, but in the middle of the video I decided it's quite good so I opened it in the main window. At this point the tracking code glitched out and the video started where I left it off in the incognito mode. Couldn't reproduce it since though.

When you share a video, you can include the time code in the URL. That’s probably what’s happened. Doesn’t seem like a plausible "glitch".

Your comment made me curious if/how Google uses incognito data. For example, if I search for a gift for my wife in an incognito window, will I see ads for this product category in regular Chrome?

BTW, interesting word choice: from Latin incognitus "unknown, not investigated."

https://www.etymonline.com/word/incognito

"Incognito mode just means they clean the dressing room after you use it. It doesn't mean the dressing room has a door."

Incognito mode isn't as incognito as normal users might think.

If you have at least a little technology knowledge it should be clear what that mode is.