May be you speak other languages fluently, me not. I you are fluent in spanish, we can continue in spanish.
The prove has been provided by lleachii.
The private key of the router seems to be encoded in the QR code.
It should not. A private key is private to a device and it should be given to nobody else.
It seems that the programmer has coded the QR code as a backup of wireguard interface.
We have other ways in luci/openwrt of making backups of the router configurartion.
The QR code is used to make the configuration of peers easier.
Wireguard is not easy to configure, because you need to give the public key of the peer device to the admin. QR code/config file makes it easier to provide your user the config it needs. But you need the public key of his device.
Having to provide an IP address for each device (with no dynamic IP supports) is not fancy either.