This is not data loss sense we talk about for Kafka or other queues, however, since the messages have not been acked: the state of unacked messages is completely unknown and no guarantees are made about them.
We weren't necessarily talking about that at all but whether data "lost" because a client crashed before it received acknowledgement of a durable write from the server is somehow the same as losing data that has been acknowledged by the backend.
I argue they are not at all the same: it is, for example, the difference between getting an error when you try to place an online order and getting a successful confirmation but the order is then silently lost.