From past experimental experience I don't believe that the impact velocity was high enough to get a visible flash and I'm rather surprised that the NASA folks thought they would see a visible flash.
If I understand it correctly, the impact velocity was about 1.6 km/s. It is know that impact flash intensity is proportional to impact velocity to the 4th power! And the peak color shift towards the visible as the velocity increases. A 30-06 round travels at 0.8 km/s and wouldn't give a visible flash impacting steel, and I don't believe if you double the speed you'll see a visible flash either. From experience you'll probably have to get to 4+ km/s before the flash gets visible.
While an infrared flash is probably, without fast infrared detectors, they might not catch it either.
We'll eventually see if they saw anything, and if the did see a flash, I'll really be surprised if they can figure out was they saw because it is unlikely they had the proper on-board instruments to make that determination.
Been there, done that right, succeeded doing it 3 decades ago on a DoD project.