Fire Carnival

I just did the Repair Job affinity mission with Lin and at the end, she "learns Fire Carnival".

The thing is...I've had Fire Carnival for Lin since, I THINK, level 3. And I've already upgraded it a couple times too!

I thought it was weird, so I looked online and every post says you only unlock it by doing the affinity mission. Did the game somehow mess up and just give it to me early? I find it hard to believe that for such a long mission all you get is an Art that you'll DEFINITELY already have once you're capable of completing that quest....