Jio is doing Deep Packet Inspection for a long-time now which isn't really practices by any of the ISP. This is one of the way to drill-down the data and alter your experience.
Jio must stop this since it's against the privacy.
No, Jio has done that since there were some rift between the Government and the Telegram Team recently after Telegram had some rift with the Russian Government.
Telegram is end-to-end encryption which is the most strongest and they don't store any of your chat cloud (if you delete the chat, it's get deleted from everywhere without showing any "Deleted" notification).
So ISP doesn't want to go against the government and hence banned Telegram.
Telegram works just fine on other ISP.