This Opera 'VPN' is just a preconfigured HTTP/S proxy protecting just the traffic between Opera and the proxy, nothing else. When you use the proxy on a different machine (with no Opera installed), you'll get the same IP as when using Opera's VPN, of course. These creds can be used with the even when connecting from a different machine, it's just an HTTP proxy anyway. (that's sha1(device_id):device_password, where device_id and device_password come from the POST /v2/register_device API call, please note that this decoded header is from another Opera installation and thus contains different device_id and device_password than what is shown below) When loading a page with Opera VPN enabled, the browser sends a lot of requests to with Proxy-Authorization request header. It's an HTTP/S proxy which requires auth. The browser then talks to a proxy (when VPN location is set to Germany), it's IP address can only be resolved from within Opera when VPN is on, it's 185.108.219.42 (or similar, see below). When setting up (that's immediately when user enables it in settings) Opera VPN sends few API requests to to obtain credentials and proxy IPs, see below, also see The Oprah Proxy.
