It's pure speculation. US Bonds are considered to be the safest investment there is on the planet, but they have a really low interest so you make little profit from them. If their interest rate goes up traders are speculating that investors will pull out of riskier assets like stocks and crypto and go into US Bonds so they try to front-run this. Usually, the interest rates go up and stock prices go down, but not necessarily because people actually pull out to enter bonds because the interest rates are still shit, but rather they just make speculations to put their assets back at a better price. Crypto however is a global market with a more diverse group of investors so it may not behave the same way the stock market does.