I experienced this once. We were at a going away party for my roommate, and they gave all the women a "ladies' menu." Well, all I can say is once the "ladies" figured it out we all demanded men's menus. I remember the waiter was put out, but we were appalled at the sexism. I'm surprised they still exist in restaurants.
Of course, in our OP's story, there was no sexism. They asked, "who is paying*?" And they gave the menu w/ prices to the person who declared him/herself to be the host.
They didn't just assume that the man was the host; they asked.
I'm not surprised that they still exist, and I am pleased to hear that there was no sexism in the OP's friend's situation.
*I agree w/ shhh it's me that asking who is paying
is the *wrong* question; hosting is different from paying. So maybe the question should have been, at time of reservation, "Are you entertaining guests? Will you need a host's menu?" So that the dad could say, "Oh, there's no need for that" and get menus with prices for everyone.
Or this, from shhh it's me:
I would have thought they would have come up with a better way to ask like " ..and is the gentleman hosting this evening?"