If something has a default password, default private key, or trusts a default public key, and that isn't clearly documented, that seems like a backdoor to me. It would be an undocumented way of Huawei or random hackers taking over your device.

And even if it's documented, although it's not a backdoor, it's still generally bad for security. Any device with non-unique default passwords or default keypairs will generally have hackers scanning the internet to compromise them. The keypair should be randomly generated on first use. The device should prompt for what password to use on first use.