It's too bad you had to go through that. There is no short supply of ignorant morons that assume all people who require special consideration/courtesy for health problems are in a wheel chair.
I hope you don't have to deal with this kind of stupidity again. Personally if I were the cast member i would have "professionally" but firmly told the guy that "not all guests who require assistance need to be in a wheel chair, unless you have some kind of official medical records on this guest perhaps you should move along and continue enjoying your day in the park."
I know, I know, probably too confrontational for DLR, but I swear I would say it professionally and with a huge smile!