It appears that another copy of the Custom game editor was editing a game, but crashed. It has left behind some temporary files that appear to be a copy of the game.
HOWEVER, the original .rpg file has been modified since then in some other way! This means the temporary copy might be out of date. Maybe you overwrote the .rpg you were editing with another copy from somewhere else?

"Loaded or last saved by Custom": This is the time when either you loaded and started editing the game, or saved the game using "Save and continue editing".

"Last edit": This is when the final unsaved change was made to the temporary files. If this is equal or nearly equal to the last loaded/saved time, then you should be able to safely delete the temporary files, because it means you didn't have unsaved changes.

"Modified" (since loaded/saved): This is the current last modification time of the mentioned .rpg file.

Options:

'DO NOTHING' quits.

'RECOVER temp files as a .rpg' creates a new .rpg file out of the temporary copy. Your existing .rpg isn't overwritten. The new .rpg file might be corrupt, so never overwrite your old copy; keep it as a backup!

'ERASE temp files' deletes the temporary files. Choose this if you think there aren't any unsaved changes worth saving.