What's the minimum amount of "gas" that has to be present to be considered "atmosphere"?
There's evidence of earlier outgassing on the lunar surface.
Did any of the Apollo missions think to bring back samples of the atmosphere?
It's not the amount of gas, it's whether the gravity is strong enough to hang onto it. There are always trace amounts of gas in space but it is only considered atmosphere if it is held by the gravity of a body nearby.
Doesn’t atmosphere require gravity? The moons is like one sixth of earth’s. Less atmosphere to start and nothing to renew it.
No oceans, no lightning storms, no plant life, no volcanoes (anymore)=no atmosphere.