I don't think this is related. This is just public key verification, the kind that other E2E messaging apps already had. I don't know about the specifics but as I understand, Beeper Mini could implement this too if they want to.
Theoretically the two are orthogonal. There's no reason why Beeper wouldn't be able to implement contact key verification; there's no hardware attestation component to it, as far as I can tell.
Practically, the added complexity of having to integrate with iCloud Keychain certainly won't help.
https://www.macrumors.com/2022/12/07/new-imessage-apple-id-s...