In "how to Eat an Ice-Cream Cone" why does the author caution against letting the cashier hand you other people's cone?

In "How to eat an Ice-cream cone" the author cautions us in letting the cashier hand to us other people's cones because it might get contaminated as the cashier is in charge of the store's money and there is a lot of bacteria on money. The cashier must wash their hands before making the ice-cream and after giving money.