Thanks for the all of the replies! When I called the mother to RSVP, she apologized profusely for the time of the party, but (as many have guessed), that was all that the party place had available. I am understanding about that - I figured DD would sleep really well after that party!
DD attended another party at this particular venue (it's a bouncy-castle type place) last year, so I know that they do allow and provide food. This child is a classmate of hers, but we don't really know the family; she's not one of DD's good friends, and she's new to the school. Again, I was just surprised....DD has been to several parties now that did not fall within specific meal times, and food was still provided. Also, because these kids are so little, dropping them off at the party is not an option, so most of us feel that we should provide a little something for the adults to eat as well. Again, a slice of pizza would've been fine.
And to be honest, I was a little miffed. I think DH felt that it would be awkward to leave, but had I been there, I might've politely excused ourselves and taken my daughter home for dinner.