Which reply did you hit? Was it the one at the bottom right corner of the last post? That’s a reply to that post. If you somehow also hit the quote bubble at the top left of the editor, that would contain the last poster’s quote which would explain why Thudlow_Boink’s quote would be in the post.
If you hit the reply at the bottom of the thread next to the flag button, that might be more puzzling.
That’s easily explained, I think. You and DPRK posted at the exact same minute based on the time stamps. DPRK saw your post within the 5 minute edit window and added your quote to their post and added an ETA to show that it was edited.