What did they explain about the cheaper breakfast when you checked in? It sounds like when you arrived for breakfast in the morning, it appeared to all her self service with no staff member around to ask which version of the breakfast you were taking.

I've seen hotels that have a cold and hot buffet breakfast offering, with the hot items on a different table. If you don't take anything from the hot table, you pay the cheaper rate, although often you're asked about this (requested to declare your choice at the beginning) or told how the system works when being shown to your table.