There was a maverick researcher in the 1960s who claimed the Lunar Maria showed signs of being actual sea-beds and the load of sediment they represented produced the mascons. Since then all the evidence has confirmed the maria as lava plains and all the river-like structures on the Moon are from lava-flows not water.

An atmosphere could have last for a time on the Moon, if it outgassed. However high energy asteroids & comets don't accrete a lot of mass on to the Moon - they in fact mostly blow back into space - so a late veneer of volatiles is unlikely to have accumulated on the Moon. Unlike Earth, which probably gained its oceans from the late veneer according to recent research.