Same here. Sometimes I wish the web was simpler and the history API was not a thing. Or barring that, that the browser would pop up a permissions prompt when a page attempted to access the history API.
The back button in Chromium type browsers should ignore history entries added before a page receives a user gesture [0]. That did not seem to happen here!
You can try it yourself by loading a YouTube video via pasting into the URL box and letting it autoplay a few videos. The back button should take you to the new tab page. If you click anywhere on the page then those autoplay entries will not be skipped by the back button.