Too simplistic
This seems too simplistic of a premise to me. Different languages have different strengths and weaknesses, and as a result are best suited for different sorts of tasks -- that, at the heart of it, is why discussions about "good" and "bad" languages are suspect right up front -- a given language can be the best choice for one sort of task and the worst for another.
If you're using a language for a task that it isn't well-suited for, you're going to have to write more (and more complex) code in order to make it work. I would expect that doing this would result in a higher defect rate. Using the same language for a task that it's designed for means that you'll have to write less (and less complex) code, which I would expect to result in a lower defect rate.
A study that just tallies defect rates with language use, but fails to take into account whether or not the language was suited for the task, means little. I would expect that sort of study would average out the defect rates and result in more-or-less the same "quality" score across the board.
Which appears to be the actual result in this study.