It is not that simple. Right now interest rates are extremely low, so what you said is likely to be the case. On the other hand, as the economy improves credit risk will decline, and lower credit risk can drive bond yields lower (this is exactly what happens in the high yield market), which is more or less what happened for three decades beginning in the 1980s.
If the US economy is going to do well, bond yields will be going up. That means a bond short position will pay off.
Being short on bonds is basically financially almost exactly the same thing as borrowing money.
(The US treasury is 'short' on T-bills. They have to essentially 'buy them back' when they become due.)