Further, “just works” Bluetooth encryption is not vulnerable most of the time. It’s only vulnerable at the instance of pairing.

It shares exchanges a pre-shared key one time at pairing then trusts that both sides will remember the PSK.

So long as you pair while there is definitely nobody around and sniffing Bluetooth traffic, it’s an excellent system.

But the author clearly wanted to go through the effort of implementing Duffy Hellman for this.