I'm sure that the local tire place could back him up on this.
they'd like to sell two tires.
but seriously. i wouldn't run two differing size tires on the drive axle of a FWD car. Think of the diff man, think of the diff.
so if they want to be super cheap asses they need to put that junk on the rear axle matched with your deepest tread tire, but then that completely hoses your tire rotation scheme.
so screw them, she hit you, it's their responsibility to make you whole and have a well kept, well maintained car like you had before, and that means they're buying two tires.