If it were birthed it might be smarter to say orphaned or alienated or something that follows the parentage metaphor instead of unmoored.

If it were berthed it would make more sense to be something like "The destiny of all books is to become unmoored from the time where they were originally berthed".

But it is more common in English to use birthed as created than this kind of extended nautical metaphor.

And it is more common for people to mix their metaphors, especially when they are trying to sound clever.

Therefore I think they mixed their metaphors a bit.