"a business entity with an aggregate turnover up to such amount in the preceding financial year as makes it eligible for exemption from registration under the Central Goods and Services Tax Act, 2017 (12 of 2017)"
So according to the notification, if you're not registered/required to register in the preceding FY then such business entity is exempted.
Two possibilities:
1. They business entity was registered in the preceding FY and this year they canceled the registration and thereafter again registered just to discharge RCM. [Very unlikely]
2. The business entity was not registered/required to register in the preceding FY and register itself in this FY just to discharge RCM (if this is the situation, then they are registered under mistake). If this is the situation, then in my view, approach Hon'ble HC and give a shot. Imagine unnecessarily the business entity will discharge GST liability now.