Jio phones appear to run a mobile OS that is not supported by whatsapp. Effectively they are using his server to host the whatsapp instance and then only deal with the very front end of the whatsapp code natively.
So I'm pretty sure what they want is to access the Whatsapp web interface and use Browserly for user agent spoofing, circumventing geographic blocking or some kind of blocking on their phones like a 0.0.0.0 entry for whatsapp.com in the hosts file. Either way it's a major dick move if you ask me, especially when there is no shortage of services built for this exact purpose.