If the address is their legal address and it doesn’t have a name on it, I could see them opening it. What I think is messed up, is them not saying anything to you about it and waiting for you to ask them about it. What’s even creepier is the wink and the “have fun”. It’s very inappropriate.

You getting a vibrator is nothing to be ashamed about but I can see you not wanting your landlord involved at all with this. What they should have done was sealed it back as best they could. If it still looked opened, left a note apologizing(letting you know they are sorry for unintentionally invading your privacy) and telling you that you don’t have to discuss the matter at all. It was up to them to make it not weird.

Anyway, don’t worry about it now. Vibrators are totally normal. I hope you got a hitachi magic wand. It’s king/queen of all vibrators.