Bitcoin has its market with buyers and sellers. In this market, there are buying and selling demands and price rises if demand on buying is bigger than demand on selling.

Minting Tether USDT stable coin gives the market a new source of capital, that will be used in the market. It is logic to think new USDT supply will be used for buying and price will rise consequently.

If they need to dump the market, they don't need to mint more USDT stable coin.