Yeah, this clearly does not belong in the Serial Monogamy pool. I'd remove it myself, but I can't figure out how to remove images from a pool.
The two methods I find easiet; either go to the pool and click Edit then remove the post number (if it's the last post in the pool it's at the bottom of the list) or edit the tags of the post and "add" "-pool:#". You can also use the pool name instead of its number but that's a bit clunky.