What does bowchickabowwow mean?

It really doesn't have a meaning. It's what can be called "scat singing," where the singer makes up syllables to fit into the rhythm of the song. Some syllables are just nonsense sounds, but they are catchy and people remember them. This is especially true in pop songs. A good example is an oldie from 1971, "Chick-a-boom," which contained these lines in the chorus, "Chick-a-boom, chick-a-boom, don't you just love it?" There is no evidence that "chick-a-boom" had any deep meaning, but it sounded good in the song.