Chances are, the agents had no idea. They jump from gate to gate and, from what I can tell, just communicate what they're told.
In the past, I've been told by agents that my flight was cancelled because the inbound for another flight was delayed so they used "my" aircraft to cover that flight (happens on YEG-YYC alot, they consolidate flights in the winter). That being said, the agents RARELY announce this - Its what I'm told when I go to the agent and start asking questions
I don't think agents purposely lie very often. I think its probably misinformation or if it actually a lie, its probably to avoid an angry mob!