More likely the US has known about the Xianglong since around the time that its development began. It has been public knowledge that they were working on it for at least 13 years now. Its capabilities would be very unlikely to surprise at this point. Globally the UAV space is well understood and mostly incremental, nobody has unleashed anything too surprising or radical in the field since the Global Hawk 20 years ago. The odds are the US military understands well what China's UAVs can and can't do, without requiring these flights to inform that particular aspect. The Navy probably appreciated getting an opportunity to track it however.
https://en.wikipedia.org/wiki/Guizhou_Soar_Dragon