I find it common for human customer support people to give inaccurate information. I don't know about "outright lying", but I've had people tell me things that are factually incorrect.
However I would not expect an airline customer support to make up a completely fictional flight that has never existed. Maybe they could confuse flights or read a number wrong, but making one up?
Case in point, I asked my bank if they had any FX conversion fees or markup. Guy said no. I asked if there was any markup on the spread. Said no. Guess what? They absolutely mark up that spread. Their exchange rates are terrible. Just because there isn't a line-item with a fee listed doesn't mean there isn't a hidden fee in there. He's either incompetent or a liar.