The technology acts as a motion sensor that detects faces, so the machine knows when to activate the purchasing interface
This sounds like an excuse to me. I'm a university student in the UK. Our vending machines use a very effective means of letting the machine know we're ready to buy something without using any facial recognition software at all. What we do, right, is press the letter and number buttons that match up to what we want to buy. The machine says how much money the item costs, and then we tap our bank/credit cards to the contactless card reader, just like we would in any other shop. Then the machine dispenses the item.
It's really, really clever how they've invented this way for us to purchase afternoon snacks to help us cope with how annoying our classmates are, and we don't even have to have our faces scanned! Truly the kind of innovative technology you'd expect to find in a university.