I don’t have a legal background, nor is consumer law part of my job, but my (admitted limited) understanding of these matters is that when registering for the account, you will have made an action - sometimes a tick-box for example, or tapping a labelled button - to acknowledge that you have read, understood and accepted the terms and conditions of the services. Therefore I believe that it is your responsibility to check if you are covered.
Having a Premium or Metal account with Revolut doesn’t guarantee eligibility for the travel insurance. From the General Terms of Service 
:
OVERSEAS TRAVEL INSURANCE
31.1. If you are a Premium and/or Metal; User, you will, if you qualify, benefit from the Overseas Travel Insurance (…)
Having said that, I completely understand your frustration about any restrictions not being more visible. Perhaps this could be included in a summary or FAQ page going forward.