Would the impact result in sufficient gas expelled from the vaporization of the meteorite to carry sound waves a distance of a kilometre from the impact? Would the blast wave be sufficient to injure an unprotected astronaut?
It depends largely on the speed at impact, which could vary widely. If it's in a similar orbit to the Earth/moon system around the sun, catching up with the Earth/moon around the sun and the moon around the Earth, that would be pretty bad a kilometer away. The ejecta could certainly turn an astronaut into an astronaught.
On the other hand, if the meteorite were coming in from a different direction, say it was orbiting the sun in a similar orbit to the Earth/moon but in the opposite direction, the speed at impact could be as high as 135,000 miles per hour, or 37.5 miles per second. It would be a spectacular show, launching fragments of the moon into orbit around the Earth and likely beyond. Not a lot, but some. Your astronaut 1 kilometer away could never survive.