I'm not familiar with that song lyric but I did google it. I would say that in that context "freak" means a person with a powerful libido. Rick James' song "Superfreak" would be an earlier example of this use:

She likes the boys in the band
She says that I'm her all-time favorite
When I make my move to her room it's the right time
She's never hard to please

...she's a superfreak, superfreak
she's super-freaky