Objects move pretty fast in space, usually tens of kilometers per second.
A 20 meter of diameter object with velocity of 10000 mps is pretty deadly impact from Earth's point of view.
Not really, the https://en.wikipedia.org/wiki/Chelyabinsk_meteor was 20 meter diameter and hit the atmosphere at about 20 km/s. While there were some ~1500 injured people, the Earth as a whole did not really notice.
I don’t know about you but I’d consider a Hiroshima-scale explosion pretty deadly. We just got lucky it didn’t hit the middle of a major population centre at a more direct angle. That could have been catastrophic.
It would suck to be in the area, yes. But the comment I was responding to said "pretty deadly impact from Earth's point of view." Hiroshima-scale explosions don't make an appreciable dent in the Earth itself, and any human population outside immediate vicinity will still be fine.