ProtonVPN passes too which is funny because I'm solving so many captchas I could power an entire captcha solving saas all by myself. So I'm not entirely convinced by this method.
That's because most sites serve you a captcha based on your IP address and ASN.
Mullvad uses both OpenVPN and Wireguard
And the site seems to tend to detect mullvad's wireguard as 'openvpn' while mullvad's openvpn is undetected by it. Perhaps that's what the parent is referring to.
That would make sense because it didn't detect Mullvad's openvpn for me.