The GP is actually right here, Signal keeps the call log in the message history (deleting the call entry from the message history deletes it from the call log), but the disappearing messages setting doesn't get applied to the call log.
It's weird to see a bunch of messages, a call, more messages, and a day later the messages around are gone, but the call remains in the history. They could have just applied the disappearing messages settings to the call entries too, as it would be natural to do, and this problem wouldn't exist.
I don't think it's malicious, because what the server knows is independent of what the UI shows, but it's a very odd UI issue that does reduce privacy.
They keep it in the UI, therefore I assume in the database as well. If you delete a call entry in the message history (like you delete a message), it gets removed from the "call history" tab as well.
It's weird to see a bunch of messages, a call, more messages, and a day later the messages around are gone, but the call remains in the history. They could have just applied the disappearing messages settings to the call entries too, as it would be natural to do, and this problem wouldn't exist.
I don't think it's malicious, because what the server knows is independent of what the UI shows, but it's a very odd UI issue that does reduce privacy.