The US NRO (nat’l recon office), DSP (defense support program) and DoD have a catalog of missile launch profiles to work with based on known launches of different missile types, so I have to believe that they’re trying to see whether the energy output (based on the launch characteristics) match one of the known profiles - whether it’s one of ours or not. I’d disagree with the assessment that it wasn’t a threat to the US because it didn’t hit land because it shows that someone managed to get in position to fire the missile and but for bad aim could have resulted in a bad day for someone in the US.