It would have been visible with thermal cameras
night vision systems are , most typically, very low-light sensitive cameras that occasionally have specific-wavelength illuminators -- they aren't generally thermal cameras.
I tend to think something with a run-time like that is liquid fuel based, too.
It's likely they had thermal cameras available. There is a lot of video of police helicopters using thermal imaging to track people they are chasing.
The audio I linked to makes me think they tried to use it but couldn't see the object.