Both are right as someone who’s using google messages for E2EE RCS, you really dont need an account and you should be prompted to use without an account and if you didnt then go ahead and do what @Username2 said which is to press on the pfp icon and press use messages without an account.
However I can see why they would be concerned. I recently realized that google messages now depends on google play (and/or gms) even to use the app alone which has become annoying for my degoogled profile (degoogled as in no play services) as I wanted to use it as a traditional sms without this duplication issue I seem to be having with the AOSP one when google messages is installed onto the primary (owner) user