Yep, they were very rude.
Considerate hosts do their bests to plan a menu with broad appeal; considerate guests do their best to appreciate what their hosts offer even if it's not their personal favorite. You get extra points for asking if she or her family had any special dietary needs, and the fact that you ran the actual menu by her gives her NO excuse whatsoever to complain (even though complaining would have been rude even if you hadn't shown her the menu in advance).
IMO, hosts should plan around common dietary limitations to the best of their ability. What's common may vary from place to place, but presumably you'll know if you have a lot of vegetarians, folks who keep Kosher/ Halal, etc., in your group. But if you're a guest with more unusual restrictions, it's on you to either eat beforehand or offer to bring something you can eat. If you're bringing picky-eater kids to a BBQ, it's on you to bring something they can eat (and if this were the case, Samantha should have told you when you showed her the menu that her kids were somewhat finicky, and offered to bring a pack of hot dogs for them or something). Why on earth someone would assume, in this situation, that there would be burgers or hot dogs, and fault the hosts for not supplying them, is beyond me.