I don't think it's lack of class that would make me ask whether he could afford lobster and champagne. If anyone ordered that in a restaurant (knowing they are the most expensive things on the menu) I think it's reasonable to say, "Gosh that's expensive, are you sure you can afford?"
For one thing, if you suspect he has no intention of paying for it, then it tells him clearly he's paying for himself.
I don't think that's an unreasonable thing to do (to ask) - I would do that if I was out with a group of women. Some people will always order more expensive things if they are out with a group of people, knowing that the cost will be shared and I'd always challenge that. It's horrible to think of people abusing others financially.
In your friend's position, TheFormidableMrsC, afford it or not, I wouldn't have paid for him. No way. His intention was to rip her off. I think she could have saved her self-respect, taken the bill to the bar and asked to pay for her own food and drink. Nobody in that restaurant would've blamed her at all.
And the same goes vice versa if it's a woman ordering lobster and champagne, of course.