Quality absolutely matters, but it's hyper context dependent.

Not everything needs to, or should have the same quality standards applied to them. For the purposes of the Cursor post, it doesn't bother me that most of the commits produced failed builds. I assume, from their post, that at some points, it was capable of building, and rendering the pages shown in the video on the post. That alone, is the thing that I think is interesting.

Would I use this browser? Absolutely not. Do I trust the code? Not a chance in hell. Is that the point? No.