The HDMI update is in RoonOs - the minimal linux used by Nucleus devices and installed on NUCs by ROCK. The current production version of RoonOs is 259.
The “Roon 2.0.37 and ARC 1.0.54 are live!” announcement and the 1432 build number relate to the Roon Server application that runs on top of the RoonOs (in this case) or more generally the operating system of choice.
The Airplay2 announcement pertains to the Roon Server Application - for which the current release is indeed 1432.
I believe that you can run the early access version of RoonOs (by following the instructions in the RoonOS Early access announcement) whilst still running the production versions of the Roon Applications which is in contrast to the recommendations when running the early access applications where the advice is ‘all production or all early access’.