I think this incident is important to be a lesson, that every time we want to make a transaction, especially a Bitcoin transaction like the one you mentioned, then we should make sure whether the recipient's address can still be accessed or not, because this is really risky to lose a fund, especially if it is a large amount.

Regarding the incident, I think this is a mistake from both parties, and more precisely this is a misunderstanding, which should have been confirmed by both parties before the transaction was carried out. In addition, we can also learn that we should not take the ownership of the address we have lightly, we must keep it as well as possible, because it could be that in the future we will still need it like the incident that op mentioned.