It's probably a red that's spare so with all the blacks tied together and the extra red tied onto the switch if its not capped off at the first light when the switch is throw it could have faulted to ground. May be worthwhile opening the first fixture and capping it off to make it safe.
Sarcasm is my friend
I'm here to learn too, i do mostly commercial/industrial/new construction and this place is a great way to pick up tips on residential from some good electrical minds. Excuse the spelling, my phone has a mind of it's own.