cultural stumbling

So sometimes the differences in American and Australian culture can make me feel more socially inept than usual.

The main example is that Australians tend to tell you what you are doing with them, rather than asking what you are doing.
This catches me off guard since even in America I sometimes have trouble gathering that I am being invited to do something. So today, when I ran into my Australian boss's wife (ABW) on the street, our conversation got weird for me:

Me: ABW! Hi! How are you?
ABW: Hi, hamster_grrl, what are you up to?
Me: Oh, I am just walking around, checking out the shops.
ABW: And, you're coming to dinner tonight? (There was a slight inflection here, making me thing that I should have known about this dinner, but I had not, awkwardness ensued!)
Me: I didn't know there was a dinner tonight...
ABW: You don't want to come to dinner tonight?
Me: No, No, I would love to come to dinner tonight. I was just wondering what I was going to do as I hadn't decided what to have for dinner. Yes, I would definitely love to come to dinner tonight. (general awkward rambling about dinner)

I left the encounter with plans for dinner, which is great, but the feeling that I look like a social moron to ABW.