Unexpected and supercool editor's note subtitles
I watched Star Wars Episode VII I think and on the start scene, suddenly there was random talking in the subtitles.
Then I found out that was George Lucas, talking through the entire movie, transcribed as subtitles.
Was super fun and interesting, nice work!
Stuff you only see when getting Torrents XD
This sounds like subtitles for a DVD commentary track, which were probably supposed to be a separate subtitle track but weren't for some reason (or your player defaulted to them alphabetically).