It means Binance is running low on USD reserves and is buying more by preventing large USD outflows while continuing to allow USD inflows.

It's worth noting that Binance operates BUSD, a stable coin pegged to USD which according to their website saw a 25% reduction in net asset reserves between Nov 2022 to Dec 2022 (https://www.binance.com/en/busd) - if that trend has continued that may be why they need a short-term supply of USD.