The age of the bike is generally taken from when it is first registered. If you have worked out that it is late registered, well that’s a good bargaining tool, but only if there are significant differences between the models.
As for price, that is up to the dealer. If they ask too much they will get stuck with it.
As for a buyers’ market, a buyers’ market is where the buyer calls the price. Since lockdown was lifted, at least in the trade, it has been a sellers’ market, demand for used bikes has been high and supply low. I think that will slowly change.
But frankly I’m at a loss as to why you are getting your knickers in a twist over that add. Seems a genuine ad to me. I am toying with the idea of adding an FZ1 to my garage, but that one doesn’t interest me (lowering kit for one thing) plus it is the wrong time for me to buy.