You already mention BTC as Index but you didn’t knew who the work for that?

Binance and other exchange has this kind of bot that usually automatically adjust the price. This is already explained by CZ before when the price of Bitcoin dump to below 10K in an instant, the market maker bot triggered when someone dump huge amount that's why price go down to that extent.

This is same with atlcoin sentiment, The orderbook adjust based on the current sentiment which creates a fake volume of buying and selling when there's a trend. Just like what you explain, BTC serves as an Index while market maker use that as reference for the movement.