Partner (permanent) subclass 100 visa is a two stage process. If you want to get a permanent visa subclass 100, you first need a provisional visa subclass 309 which allows you to stay on a temporary basis till the time permanent visa is not granted.
When you are outside Australia you apply for both the permanent and provisional partner visa. However, you have to pay the fees of only one visa that is provisional partner visa.
If you are granted with the temporary partner visa then you are eligible for the permanent partner visa subclass 100 about 2 years after you lodged the application.
This means that you applied for both the partner visas when you were outside the Australia and you were granted the first visa which was temporary partner visa and after 2 years, your second stage application is processed.
However, if you and your partner are living together for many years before lodging your application, it is the strong possibility of you getting a permanent partner visa immediately after provisional visa.