Aside from the idiot Adlet's grand theory, there might even be such a mundane reason that Maura learned there's an extra brave and locked them all in on purpose to weed out that extra one. Although at the same time it has to be said she certainly didn't behave accordingly, allowing Hans declare Adlet the culpriot totally one-sidedly. Not only we don't know enough, like Moogles said, but there was so little and unbalance intelligent acting during the discussion in the temple that it's exceedingly hard to predict anything. Personally I still half hope, like I said a long time ago, that Adlet is unknowingly a fake hero created by the demon king himself to be used as a tool (since he's an idiot and thus an excellent tool). However, that wouldn't alone explain this particular mystery since we know Adlet only forced the door open, nothing more.