It's not very surprising for me, because C is a simpler language and it's easy to paint yourself into a corner with C++.

The critical question is: what does the error rate look like for code of similar complexity? It's very possible that C programmers will try to keep things simple, because the language doesn't support them and they have to be extra careful. The flip-side is that they probably can't develop projects as complex as C++ would enable them to.