Earthworms mean healthy soil. Grubs don't come up from the soil, so weed cloth doesn't have any effect on their presence. Depending on what kind of grubs they are, they may have been in the compost. Grubs are part of the lifecycle of beetles, which lay their eggs where they will have something to eat.
At night while we are sleeping, all kinds of things can get into our gardens.

Here is a link that might be useful: worms