an example: someone sent me money from a pished bank account. After some months the bank forced me to send the money back. So I had to send the money, they were not able to reverse it and I could have said "no" (but with legal consequences)
What's the difference in practice?
The bank is bigger, stronger, has more lawyers, more connections - they can force you into basically anything.
So if a SEPA transfer is technically reversible or not is uninteresting, it's the end outcome that's interesting.
Everything is tracked. Who owns an account, where's the money transferred. So it's rather easy to claw it back. Of course, there will always be some escape artists, but usually the bank gets their way. Banks tends to become quite pushy when someone owes them money.