Imagine in your example the vending machine has a variable pricing and lowers its price if nobody purchases soda. Is it theft to wait longer than the designers thought people would wait and purchase the DRNK at price lower than the machine owner thought they would.

I think a better example is a claw gambling machine. You pay Fiat for a chance to grab fiat out of a pool.

If you come up with a strategy whereby you can grab more or all of the Fiat in a way that the game/machine designer and other players did not anticipate, is that theft?

Alternatively, people are playing a modified version of Poker with rules they don't understand, and someone understands the rules better and gets their money, is that a crime?