Let's break this down:
Tangsuan was "highly allergic" to dairy and nuts, and they chose that particular restaurant in part because of its promises about accommodating patrons with food allergies, according to the lawsuit filed in a Florida circuit court.
They chose the restaurant because of incorrect/misleading information on Disney's site. The site is subject to the same blanket TOS as most of Disney's online portals.
The complaint details the family's repeated conversations with their waiter about Tangsuan's allergies. The family allegedly raised the issue upfront, inquired about the safety of specific menu items, had the server confirm with the chef that they could be made allergen-free and asked for confirmation "several more times" after that.
"When the waiter returned with [Tangsuan's] food, some of the items did not have allergen free flags in them and [Tangsuan] and [Piccolo] once again questioned the waiter who, once again, guaranteed the food being delivered to [Tangsuan] was allergen free," the lawsuit reads.
The restaurant made a terrible, deadly mistake. That was the crux of the issue, and trying to argue that they wouldn't have eaten there in the first place had Disney's website explained that the restaurant was not likely to accommodate their specific needs is the kind of logic only an ambulance chasing lawyer would use.
If you have life-threatening allergies, it is on you to make sure the restaurant can accommodate you. You can't have it both ways - if you know your allergies are serious and you know you're going to verify with the restaurant, you really can't claim that incorrect information on the website was truly at fault. If the restaurant swears up and down they can accommodate you and then fail to do so, you (or in this case, your next-of-kin) has a case against the restaurant itself - not its landlord.
Look, Disney gets things wrong often enough. If they had argued that Disney's TOS means you're SOL if an alligator kills your kid on Disney property, that'd be a whole different ballgame. But this was an independently owned restaurant that screwed up badly, and the lawyers saw the potential for Disney-sized dollar signs.