The author defined it after responding to comments--he says it's bugs per repo. So, a repo with 10 lines of code and 1 bug is, according to him, less buggy than

The author defined it after responding to comments--he says it's bugs per repo. So, a repo with 10 lines of code and 1 bug is, according to him, less buggy than a repo with 100 lines of code and 2 bugs. Also, note that projects in dynamically-typed languages tend to be smaller since people tend to switch over to static types for larger projects. So this 'analysis' is pretty much designed to 'find' that dynamically-typed language projects are less buggy.