I've had this happen a couple of times over the years. It's very disconcerting to say the least.

As far as propping doors open, that's standard. Most housekeepers don't have the door shut while they're in the room - unless they have the TV on while cleaning.

I don't think it's a big deal that they used the deadbolt. They could have propped it open with a wedge/door stop or something else. The problem was they left the door open and never came back.