I agree that USDT is fishy and it may be behind a large percentage of the gains in BTC and the other coins.
However, there is also another possible explanation. When investors want to buy BTC they first to go Binance and ask for USDT in exchange for USD. Binance creates new USDT for them. Then they use the USDT to buy BTC (reverse causality). Just saying it's possible, but I believe Jacob Oracle to be right.