While the article indicates there is a Quantum here, I found two Nuka Cherry instead in the pile of rubble in front of the Nuka machine.
There should be three colas spawning here, and there seems to be some randomness involved. I found a Nuka Cola Quantum and two plain Nuka Colas. In your case, the third cola probably clipped through the floor. Wouldn't be the first time this sort of thing happened in a Bethesda game.