i now join the ranks of RiverKilt

[Chef]

I wonder what the point is of a casual day if management can still dictate some kind of dress code.

Casual rarely means "whatever you like" in a business environment. Most large companies still have policies that cover casual days. In fact due to the variety of casual wear and the problems enforcing it many companies are starting to go back to "business attire" rather than deal with their employees idea of casual.