Oof, never thought about this one. Do we have systems in place that would quickly and reliably differentiate an unexpected asteroid impact from a nuclear strike?
That's perfectly correct grammatically. It just means whoever wrote that pronounces it N-E-O rather than "neo".
As to your question, I think yes since I expect the trajectory would be very different.
I think they’re more referring to ‘if an asteroid hits Washington DC, Moscow, or Beijing in the middle of what is going on now, will everyone check their satellites for it before they launch a retaliatory strike?
The concern raised in the paper, which I now share, is that in the time between initial detection and someone running the tape to count the flashes, nukes could be launched. Particularly for powers who have invested heavily in use-it-or-lose-it land-based missiles. You need that differentiating infrastructure and protocol in place ex ante if it's going to prevent false retaliation.