If you discover a reproducible flaw in a blackjack game -- the card shuffler at a certain table isn't random -- is there a penalty for that? Because just having a computer in the mix doesn't seem like it really changes the moral equation.
The real argument is not if pushing the buttons in the right order is cheating, but is it hacking? That issue seems to come down to whether or not there was an escalation of access. Did those button presses give him unauthorized access to data? He exploited a flaw to alter the payout of the game, and that is at the very least fraud. If we are using your blackjack analogy this is like he somehow Jedi mind tricked the dealer to change the payout for a 21. If I used a software exploit to get a bank computer to double my money I have no doubt that would be seen as hacking. So how is the gambling machine different?
From the article:
"Now when Kane returned to Triple Double Bonus Poker, he’d find his previous $820 win was still showing. He could press the cash-out button from this screen, and the machine would re-award the jackpot. Better yet, it would re-calculate the win at the new denomination level, giving him a hand-payout of $8,200."
To me it seems analogous to placing a $1 bet on a table game, then swapping the $1 bet for a $10 bet if your wager paid out. That kind of cheating/fraud is fairly commonplace (and dealers are trained to prevent it).
If e.g. someone found a way to log in as other users, that would reflect poorly on the bank's security, but it wouldn't entitle them to withdraw all the money they could access, even through "a sequence of buttons that they were legally entitled to push."
I think categorizing it as hacking makes sense in that light. The issue seems to be that the current laws treat hacking as an exotic crime with federal scope, which makes the legal cases a bit quirky.
When I was a teenager, an ATM once reported my checking account balance had a few extra thousand dollars in it. Withdrawing that money would be fraud, even though it was a computer error. Luckily I was not a stupid teenager and I left it alone. The next day it was back to the correct value.