Nothing private! The rewards data come from Nodely. I also use the NFD API to convert an NFD to its Algo address, and Binance to get the current Algo price.
You can actually open the Chrome DevTools (right click > Inspect > Network tab) and see the API calls, it’s pretty cool!
It’s also open source, so you can check how it works: algonoderewards/src/hooks/useBlocksStats.ts at main · cryptomalgo/algonoderewards · GitHub