Up along with the search bar there's popular search terms, and that's one of them. There must be someone else making search keywords for images.... thats really effing stupid
Here on the forum you can add tags to any thread but not an individual post or image. When the Google bot or other bots are crawling the site they will pick up these tags unless there is a robots.txt file that limits what pages they scan. The thread may have had tags or those words in it.
After deleting the images it will eventually disappear.
I google that term that I don't want to associate LPF with, and your image doesn't show up... proves google's superiority I guess
Joking aside, hopefully that disappears soon.