No, you’re not missing anything. Adding a railcard discount to a 60+ Oyster is pointless.
You will need to buy a normal adult Oyster and get the railcard discount added to that.
As a final note, whilst brfares.com is brilliant for finding fares for the National Rail network, the Oyster and CPAY fare info is not always correct. This is not the fault of brfares. There is no direct link between the data used by brfares and the TfL database which means that the fares can sometimes be wrong. There are also a lot of missing fares.