That is a bit of an overstatement. Accommodation should be considered if they provide the same or greater level of safety. Both side are actually misinterpreting ADA.
For the families part, they should have proposed a way that their child could acess the parks with out creating an health hazard (assuming there is one)
For Disney's side, as blanket one size fits all rule with no path to viable accommodations is also not allowed.
Disney probably did a technical violation by the wording used by the CM, but not a direct violation of the child's rights because no accommodation, that would not create a health risk was requested, therefore Disney did not deny a reasonable accommodate under ADA.