Questionable answer in the Example Test on UI design

I was looking into the sample test of your certification program on UI Design and I think the answer to the 2nd question is arguable.

Plus icon is as versatile as the star icon, if not more:
- Haven't you seen FAQ accordion blocks that open by clicking on the plus sign?
- Even the Example Test was opened in the Google doc UI, with a plus icon on the top bar where it allows to zoom in. And the similar one in the settings of the Chrome browser dropdown menu.

I find it easier to get all listed cases of the star icon to indicate the "favorite" meaning - rating shows how much you like the thing in gradations, premium-only is the favorite of the stakeholders :D

I would kindly ask you to reconsider either the Icons listed in the question, or the answer to that question.
I would also like to hear your thoughts on this matter.