This guy was apparently obsessed with video poker. He played constantly and knew the game inside and out. Apparently he stumbled across a bug, and was able to repeat the necessary steps to reproduce it.
I think this is more like an obsessive video game player, who plays the game enough to learn every trick and secret. For example, say there is a particular game boss you wish to defeat. Play enough, and you learn the boss encounter by heart. You will know what the boss will do and when. You will learn where to stand, what abilities to use, how to cheese it, everything. Eventually, you will be able to beat in your sleep. Is that hacking?
To me, hacking would be modifying the software or machine or obtaining the source code to find exploits.
This is stealing, like taking advantage from a malfunctioning ATM machine to obtain lots of cash is stealing. If you take money from a malfunctioning ATM, is that hacking? It is not.