Forgot to Lock her up

I came home last night and Maui was on top of her cage and her cage door was open. I must have forgotten to lock her up when I left. I am so glad it wasn't Manzi who was out. I looked around the house and didn't see any signs of her wandering around, not even droppings. I am not sure I believe that she was sitting quietly on her cage all day either.
This morning, Manzi got into trouble as I was getting ready, so I locked him up while I went into my room to change. I heard Manzi and Maui threatening each other (they make a noise most comparable to the "whooo" from an owl to threaten each other; I'm not sure who taught who that noise, but it has turned into their threatening noise and I can be sure that when I hear it, one or both Greys are fluffed up either at each other, or at another person). I went to look at what was going on and to my surprise, I saw Maui on top of Manzi's cage. Manzi was climbing, but staying a safe distance as she will bite his feet (they both quickly figured out that they can bite each other's feet to do harm). I put a piece of cardboard between the bars of the cage to keep Manzi from biting Maui's feet and pulled her off the cage. Usually Maui is not the aggressor. Anyway, I was wondering if this happened yesterday while she was out all day.