I extracted some videos from YouTube (using y2mate) about a week ago of guitar lessons from a player named John Redbourne in case they go missing. I saved them to my local hard drive in a folder called "Redbourne Guitar" and the files are named after the songs, like "Salisbury.mp4" etc.
Anyway, I just watched one of the videos from my hard drive, and lo and behold, when I connected to YouTube, my recommended feed was full of videos from John Redbourne. I haven't researched or done anything online about John Redbourne since I downloaded the videos. How did YouTube know I watched it?
Use of Windows 10, Firefox and the video played with the default application "Movies and TV" supplied with Win 10.