No, it means that if you approve a device to link, and you later have reason to unlink the device, you can't establish absolutely that the unlinked device can no longer access messages, or decrypt messages involving an account, breaking the forward-secrecy guarantees.
That leaves you with the only remedy for a signal account that has accepted a link to a 'bad device' being to burn the whole account. (maybe rotating safety numbers/keys would be sufficient, i am uncertain there) -- If you can prove the malicious link was only a link, then yeah, the attack i described is incomplete, but the issues in general with linked devices and remedies described are the important bits, I think.
That leaves you with the only remedy for a signal account that has accepted a link to a 'bad device' being to burn the whole account. (maybe rotating safety numbers/keys would be sufficient, i am uncertain there) -- If you can prove the malicious link was only a link, then yeah, the attack i described is incomplete, but the issues in general with linked devices and remedies described are the important bits, I think.