You can see lucy_gothro’s wikipedia content is appended to the article text. It’s not just oneboxes, though, I’ve seen just a straight text comment either append to, or completely replace the article text.
I’m on Firefox 53.0, windows 8 currently, but I’ve seen this on older versions of FF, and windows 7 at least.
Thanks, this will save me a lot of head-scratching, as I always spend way too many valuable person-minutes trying to puzzle out what extremely subtle joke the first commenter is pulling by copy-pasting the article into their comment…