Also, many quiz items are far away from the specialities of C++. It's stuff like duplicate expressions. Or a variable being subtracted from itself. Or a variable assigned to itself.
Startup idea - Generalize this in a gamified form as a vehicle to assess the caliber of programmers for potential employers. (Hiring is expensive - recruiter bonuses are 5 figures in tech, plus the opportunity cost of lost business if you don't have the capacity to handle growth).
But these are real bugs from real software, which in this case happen to be taken from a corpus of C++ code. The game specifically claims it's not about knowledge of C++!