DESKTOP WEB: Why did Reddit randomly bring me to this thread while I was browsing a completely different subreddit?

tl;dr I was browsing r/radiohead and opening threads that interested me in new tabs. Later, I went through to read each tab. One of them was this thread: https://old.reddit.com/r/Artadvice/comments/1ujddh6/what_can_i_do_to_make_these_characters_more/

On a subreddit I have never visited and a thread that was certainly not cross-posted to r/radiohead.