The index price is from centralized exchanges or swaps and protected by Chainlink.
Type A crypto assets, which have price in major centralized exchanges like Coinbase and Binance, the index price will be a weighed average from centralized exchanges. There is mechanism to eliminate the offset data in extreme circumstances and Chainlink further protects the price data.
The weighed average price is then pushed on chain through Oracle.
The price heartbeat is 20s and deviation threshold is 0.1%.
Currently the Type A crypto assets include ETH and Matic.
Type B crypto assets do not have a valid price in major centralized exchanges. The price will come from a weighed average from different trading pairs from different swaps.