The articles about it were really too vague for me, personally, to put any faith in what the articles were saying. From what I recall (which is even more vague), it was suspected so, I believe, she was set up, and was caught. To me, being set up brings to mind having a safe left open, honestly. Other than that the articles never said how she got into the safes.
We've never come back while a room was being cleaned at WDW, but staying at the Grand Californian one time, we noticed that they were "in" several rooms at once. Which meant they left doors open. DH experienced this directly because he went back to our room while our door was open but the housekeeper wasn't in the room. He got to discover their security methods because she came back while he was looking for something in my stuff. He and I have different last names, the room was in my name, and he'd left his ID with me. That was a fun few moments for him.

Thankfully he was listed on the room, just not as the first name, so a quick call to the front desk was all it took.
But if he were quicker he could have been in and out of the room without the housekeeper knowing.
Lock up everything you can't easily replace!
And if a door doesn't close, report it immediately. Let them have the chance to fix it on THAT trip.