You’re getting confused between Roon 2.0 and ROCK. The ROCK image is the current one (remember that the version of the Roon OS that it installs is version 1.0 build 227, which is the latest build for Roon OS).
I think you will need to manually upgrade your ROCK/NUC to Roon version 2.0. Check out the last section of this FAQ, where it spells out the process of moving from version 1.8 to 2.0 for a Nucleus or ROCK system.