So many comments in this thread are saying that scientists are bad programmers, but even a great programmer can make mistakes like this. The solution isn’t related to better programmers, but instead for users to treat codes as instruments, and hence a verification and calibration step.
I would say it depends on the thought process that caused the bug. There are a couple of possibilities I can think of:
Did the author of the code simply forget to sort? That's equally likely to happen to anyone.
Did they assume that the sort order of glob.glob() was reliable across different OSs and file systems? I don't think this would have happened to an experienced software developer. At least there would have been enough doubt to go read the first line of the docs.
Did they not care whether the code worked anywhere outside their own personal setup? This is perhaps slightly more likely in an academic environment but I'm not completely sure about that. We'd have to know more about the specific circumstances.
What I find more astonishing is that it took so long for this bug to be found. It's not exactly an edge case or a rounding error. It must have caused wildly incorrect results in many cases.
So I think the more important differences may be on an organizational level rather than a question of individual competence.
