According to Quartz, Bitcoin’s recent rise appears to coincide with the creation of new Tether tokens. Some crypto analysts suspect Tether (the company) is creating USDT not fully backed by dollars and using it to buy bitcoin, driving up its price, through Bitfinex, an affiliate exchange. (The companies deny this.)
Although crypto speculation surely increased after the social media giant’s announcement, bitcoin’s recent rise might also have something to do with another digital token, Tether, a US dollar-pegged unit commonly used to trade bitcoin on exchanges that lack banking partners. Tether is issued and redeemed by a company of the same name.
https://qz.com/1654449/is-tether-a-factor-in-bitcoins-price-surge/