According to the 1988 patent filed regarding french fry vending machines, the machine's cache of frozen fries are immersed in a bath of hot oil for a predetermined length of time in order to cook them. The oil is recirculated (and hopefully cleaned - perhaps that's where the unique flavour comes from) in order to be re-used for the next batch of fries.
I have seen an old example of one of these (at the Canada Science and Technology Museum cafeteria somewhere in Ottawa, if memory serves) that dumped the paper cup, then the fries into the output slot of the machine. I made sure to use it a few times, mostly for the sake of novelty. There's a big warning light on the front of the machine telling you not to reach in until the light turns off - and the reason for that is usually that there's some excess hot oil coming along with the fries. Occasionally the cup would land on an edge, roll over and then all of my fries would land in the output slot. A tragedy, but if you're fast enough, you can take a gamble by reaching in, grabbing the cup and setting it upright before the machine starts to spit hot fries and boiling oil at your outstretched hand. The challenge and risk this provides is, I feel, unmatched by today's more servile vending machines.
From consulting YouTube, it seems there are apparently McCain-branded french fry vending machines in Austria and probably worldwide. I would have figured it to be a North American invention, in the same way that the hot ramen vending machines are uniquely Japanese.
I feel particularly bad for whoever has to clean and maintain them.