This is how the relatively new CE category enforcement system works. If you don’t have any ride history for 90 days it puts you in E category. Now that you have raced E category you will see the 20 min power you did has put you in C category. This now allows you to race in any category C or above. Of course you can now choose to race in B category.
The system was re-designed this way to stop you coming back and racing in D category. But daft as it seems you didn’t need to actually race you could have gone out and done a gentle ride and been given a D category thereby defeating the whole point of the E category !