What does a deterministic symmetric key mean?
It's saying that it is possible to have different servers with the same symmetric key values generated. This may or may not be desirable per the business. For example, you can create your own symmetric keys that match.

The DMK just protects the symmetric key by encrypting it, however once decrypted the actual key portion could be the same. This can be desirable as symmetric keys have no backup/restore mechanism on their own.