My complaint was about the deliberate and aggressive mediocrity of his work. I have at least three times his experience and he would not even engage with me, which I did politely, not haughtily or dismissively.
The most important point is that he made changes to the API without saying anything to anyone. It so happens I review all commits in my projects and saw what he had done, otherwise this might have wasted hours or days or, worse, exposed bugs to customers. To not find every row was not an anomalous case, it was not like a NULL pointer, it absolutely would happen, and we had no QA.