All I found was this comment about the difference.
Premium domain is only available when you have premium, because fewer people pay and fewer people use it, so there is less abuse and the domain name has better reputation, so when you public domain is not working, using the premium domain may be able to register.-
Premium domain is only available when you have premium, because fewer people pay and fewer people use it, so there is less abuse and the domain name has better reputation, so when you public domain is not working, using the premium domain may be able to register.-