There need not be a difference in the rule. There is a difference between Turbine not enforcing the rules versus people breaking those rules.
Incorrect, as being able to run a quest (not a raid, a quest) with one person flagged and 5 people red dooring it is intended design. Shadow crypt had nothing to do with glitching a raid so one could collect the final chests and then re-enter on the same character however.
Also incorrect. 5 group members can red door the quest with one person flagged opening it. This is not so with raids.
And Turbine chose to not enforce the rule, and clarified as such, only after years of being asked the same question over and over again.
While attempting to claim similarities youre actually highlighting the DIFFERENCES in the two scenarios, thus supporting my position. Thanks for the support.