I work for IPinfo. I am not sure what routing tricks Proton uses. I have looked into the smart routing and stealth protocol related documentation. I am not sure if Proton does anything unique when it comes to IP location. I am not saying this officially, but I am just curious here.

Smart routing documentation: https://protonvpn.com/support/how-smart-routing-works

'Virtual' VPN server geolocation involves informing IP geolocation providers that their Singaporean servers are located in India. We looked into data and latency-based locations, but the industry at large uses self-reported location information for their data. So, if you use a service that uses IP geolocation provider (that is not us) they will just tell them that the Singaporean IP address is located in India, because that is the information they have and they do not have any other ways to verify it. But at the end of the day, the location information is coming from the VPN itself.

I could be wrong, and there could be technology and technique I am missing, so I am happy to learn. The blog is written by our founder who is accessible to the Proton team if they want to share their feedback with us.