That's almost unbelievable, but I checked, and so it is. And they noted that the bond has "a variable interest rate that has averaged 3.19 percent over the past 10 years."
Over the past 10 years...but not now. I'd be surprised if that bond ever breaks 3% again.
Keeping the official inflation rate low is one of the few ways the feds can continue to afford to borrow more - by keeping payments on existing debt artificially low.