Ghost Festival refers to the day when the dead are sacrificed, corresponding to the "Qingming" day when the living are sacrificed.
Bat is an animal under Chordata and Mammals, and it is the only mammal that can really fly. Except for baby bats, most bats have a hollow saccular body cavity composed of skin membrane, which produces gliding force. There are more than 960 species of bats in the world, and there are about 8/kloc-0 species in China. Bats are distributed all over the world except some islands in polar regions and oceans, with the largest number in tropical and subtropical regions.
So, it's not that bats will fly around like your home on Halloween night.