I'm sure he knew she was there. She knows him pretty well and I don't think she'd go up there without invitation with him. I know she would with me =p. Also he's a fairly light sleeper and would wake up at least briefly when she jumped up.

It never ceases to amaze me how the dogs know how to behave differently according to the person's personality. Tasha has snuck up to lay on the sofa upstairs before. If I walk into the room she just looks at me all cute, but if she hears David coming she jumps down quick. Don't ever underestimate those doggie minds