I don’t advocate lying, but in that case at least in California I think it’d be safe to give them any number you feel is useful. After all, this is a moment of negotiation, not a moment of establishing facts, and they have already told you they’re playing loose.

[Edit] To be clear, I would break off the interview instead of playing that game, but I have the good fortune to have a lot of offers. As others have said, it’s a big red flag. But if you’re stuck with it...