Business & Hobbies with Eco Lifestyle Question

For my game, I had a sim create a small business based around the Fabrication skill since she has it at level 10. When I went to go teach a class about Fabrication, I was able to start a class for it. No problems there.

However, the game kept telling me that for the class I needed to give a 45 minute lecture on Rocket Science (which my sim had 0 levels in).  I ended up cheated my sim's skill to be level 10 in Rocket Science, but my main question is why does my sim even need the Rocket Science skill to teach a Fabrication class? Why can't the lecture be about Fabrication?

I do own a lot of packs, but I don't use CC or mods. I also play on a Mac.