The turnaround in RUH is 100 minutes. Your trip report mentioned some sort of transit option (although you couldn't use it) that did not go through immigration. They probably just use the same airplane from the same gate to head back to LHR, right? Both flights operate from T1, at least. I think I'll call BA to ask about this once the call center calms down from the weather problems. The BA site won't book a return flight at RUH as their system enforces a 120 minute MCT.