What does it mean when bats fly over my house on the night of Ghost Festival?

This statement has no scientific basis.

The Ghost Festival refers to the day for sacrificing the souls of the dead, which corresponds to the "Qingming" day for sacrificing living people.

Bat is a type of animal under the phylum Chordata and class Mammalia. It is the only mammal that can truly fly. Except for ordinary small bats, most bats have an empty sac-like body cavity composed of a membrane. This creates gliding force. There are more than 960 species of bats in the world, and there are about 81 species in China. Except for some islands in the polar regions and oceans, bats are distributed all over the world, with the largest number of bats in the tropics and subtropics.

Therefore, bats flying into your home on the night of Ghost Festival does not mean anything.