Clicking the link to that blockchain service informs you that it is "Not Available in the U.S." Some blockchain.
To answer your question - the point of a blockchain would be a universal and uncensorable key store the Telegram client can point back towards. The fact that Telegram is centralized is less important when messages are encrypted. It would still in theory offer a way to bootstrap connections with people that is less vulnerable to censorship than relying on a central server, but I don't know and won't speculate more on the details of the specific blockchain they are using.
To answer your question - the point of a blockchain would be a universal and uncensorable key store the Telegram client can point back towards. The fact that Telegram is centralized is less important when messages are encrypted. It would still in theory offer a way to bootstrap connections with people that is less vulnerable to censorship than relying on a central server, but I don't know and won't speculate more on the details of the specific blockchain they are using.