Expedia say this, but hotel pesonnels don't know anything about it? Are they lying?

I booked a room for two nights at one of the Hilton Garden Inn's in Toronto last week through Expedia.com. The online booking said free breakfast is included. However, when I arrived at the hotel, the front desk people said they knew nothing about the free breakfast and argued with me. I don't know if they were lying or what (regardless they shouldn't have argued with a customer.) I later connected to the Internet and printed my receipt on Expedia so that I could prove that I wasn't lying. They then gave me the voucher for the breakfast. What's the deal about this?