Yes, any time you can store and recover encrypted cloud archives across devices, without needing to transfer keys between devices, it implies that there is a key archive somewhere in the cloud. Even Signal struggles to get this both user friendly and properly secure without compromising forward secrecy. I believe they still actually make you explicitly do a local key transfer to populate a new device, even though they have cloud archives now. Whatsapp doesn’t do that. And the app also clearly leaks some amount of unencrypted data anyway, archives or not.