They do not use the phrase exactly-once delivery as far as I’ve seen, they say “exactly-once semantics”. And this is referring to a specific set of Kafka features that you previously had to build yourself if you used Kafka. I have not seen any reference to them claiming their solution is somehow novel. In fact, it just wraps up patterns people were doing anyway.

Oracle claiming to support serializable transactions is also false (as you say), but calling it a lie is not the whole story. “ANSI serializable” and actually serializable are not the same thing. Oracle is “ANSI SQL-92 serializable”, as in no named anomalies from the spec. There just happen to be more anomalies like write skew which are not in the spec.