That is strictly speaking incorrect. The rules are like this:
1. If the A2 national (Bulgarian or Romanian National ) had a live to remain before 2007 when these countries joined the EU, then they will be allowed to work unrestricted.
2. If they obtained work permit, then after 12 months of continuous employment, they will qualify for BR1 and have unrestricted access to employment.
3. Student 20 hours working, are not included in the 12 months continuous employment, as these people are not considered as worker, they are student, and only allowed to work inorder for the UK not to fall foul of the rule on discrimination.
I suggest you
read through the rules from page 23, thoroughly. The rules ae quite complicating, but it should improve your understanding.