Well, in this case, it was a graphical program that was doing it, and I really could've recognized that the file was being created by that. I had just kind of forgotten that I opened this graphical program a few days ago on a different workspace...
The regular ls -l doesn't show the inode on my system, though. I only realized it when I had assigned more permissions to the file and those got reset by deleting the file. The last-modified timestamp also gets updated each time, but I only spotted that afterwards...