Why is my cat randomly meowing? She jumped off the bed, laid down on the ground looked ta the ceiling and started meowing. Then she started grooming herself.
This probably isn't going to be a very satisfying answer, but: It's just something some cats do. Some cats never meow unless they need something. Some cats like to "talk" to people (and enjoy it when their human talks back to them). Some cats like to "talk" to themselves.
Think of it as your cat thinking out loud "I wonder if there's anything interesting on the ceiling."