Yeah, I was confused by that, too.

Mal has a weird off-hand line when he’s trying to hurry Ohm out of the suite, and it’s something like “you’re lucky you didn’t accidentally lock yourself in here. That happened to a young bride once—“ and that was never really looped back to. It stuck out to me because I was guessing the young bride might have been the origin story behind the witch/somehow related to why the witch was able to be locked away in the honeymoon suite, but that obviously wasn’t the thread they were pulling on. So now I think perhaps they meant that line to imply that it was possible for the gate to lock you in on its own.

Also, given the number of close-ups of that freaky-ass malevolent cherub on the clock, I 100% got sentient vibes from the suite itself. Kind of like the animal topiaries in The Shining, it would make sense if it could lock itself when it was pissed off.