A royal straight flush (aka royal flush) cannot lose or tie to any other hand in Hold 'Em. It can't lose or tie in the main pot. It can't lose or tie in any side pot. It can't lose or tie in any situation, period.

It could be that someone folded before the turn or river (and no royal on the flop), but that's not losing with a royal flush. There, one would be folding before one knew that a royal was en route. That is quite plausible, as you could have only a royal draw, and someone is making a very large bet after the flop and/or turn. Folding could well be the right move, if the only outs after the turn are the nine flush cards (one of which would make a royal).