If you know it's an error, why would you book it?
Anyone who calls something an error fare doesn't know how to play the game.
I book whatever fares are presented to me and I choose to accept. I don't know the motivation behind them, nor do I care. If I like the price I see, I click purchase.
I just bought some batteries at Walgreens for 99 cents. That's 80% off the usual price. I have no idea what their intent was there, I just needed batteries, and liked what I saw.
Same goes for airlines. If a transcon is typically $200, and I see one for $40, I may choose to buy it.
Got it?