That is exactly what I've always though happens. I'd argue that, with ATMs, since you're dealing with software that after a transaction has passed commands hardware to mechanically dispense pieces of paper that there are two different processes going on.
If the transaction passed (the human facing ATM part at least) you effectively withdrew the money, software wise you actually took it. If something happens in the procedure of actually giving you the money the machine informs something the likes of: "hey Mr. Software, something went wrong here, credit that back please". I'd argue that if everything was enclosed into one transaction you could have an edge case in which the "money transaction" passed, the cash was dispensed, something went wrong just after and you get a roll back of everything but the money was still physically withdrawn.
ATMs have cameras, so in the case that the cash was not dispensed, they can manually fix the problem and credit your account in case of a claim (they have the camera footage and the ATM's paper trail). On the other hand if everything was enclosed into one transaction, it might be a bit awkward for a bank to tell you a week later: "Hey man, we made a mistake and we now need to take out 500 dollars out of you account, but be assured we're right about this here..."
Hell people see the bank crediting you something you did not take as good customer service, but I'm pretty sure that people will complain about the bank taking money from them if it's not done at the exact moment where they took the action of taking said money out of their accounts.
If the transaction passed (the human facing ATM part at least) you effectively withdrew the money, software wise you actually took it. If something happens in the procedure of actually giving you the money the machine informs something the likes of: "hey Mr. Software, something went wrong here, credit that back please". I'd argue that if everything was enclosed into one transaction you could have an edge case in which the "money transaction" passed, the cash was dispensed, something went wrong just after and you get a roll back of everything but the money was still physically withdrawn.
ATMs have cameras, so in the case that the cash was not dispensed, they can manually fix the problem and credit your account in case of a claim (they have the camera footage and the ATM's paper trail). On the other hand if everything was enclosed into one transaction, it might be a bit awkward for a bank to tell you a week later: "Hey man, we made a mistake and we now need to take out 500 dollars out of you account, but be assured we're right about this here..."
Hell people see the bank crediting you something you did not take as good customer service, but I'm pretty sure that people will complain about the bank taking money from them if it's not done at the exact moment where they took the action of taking said money out of their accounts.