This is quite rude in fact.. however I can't see that in this situation that it was intentional. Perhaps a better way to organse tihngs if you were ever in this situation would be to make sure you are specific about the evening and dinner plans and how they work around everybody else.. after everyone you have invited is clear on what to expect you can then set a time and date to have a great time.
Hope this helps.

Okay, I would have done something like this...

OMG, I did not know we were having dinner! I thought you just said wings and drinks. My bad. Oh well, better late than never. Oh waitress...

At this point your "inviters" would be faced with the embarrassing task of fessing up that you were not invited for the dinner portion of the evening, just the after dinner drinks, etc.

Yeah, this is an immature approach but it beats harboring resentful feelings. I say put them on the spot, then when they have to say it out loud, they can't help but see how rude that was.