Fuzzing is great, but he doesn't seem to understand what a language flaw is.
In the case of Python, he's found 2 methods in libraries that can call shell commands. Leaving aside that this would be a library issue rather than a language issue, there's no evidence that it's even that.
Python explicitly doesn't have sandboxing. Like most languages (including C, C++, etc), the documented behavior is that if you control the program and environment then you're fully allowed to import subprocess or os and run whatever you want. You don't need to find "hidden" ways to run a subprocess, you can directly "import subprocess" and run stuff.
This is doubly true because of the nature of the modules investigated. The first "flaw" is that mimetools has a deprecated "pipeto" method that lets you pipe to arbitrary commands. But mimetools is already well-known to expose os access in millions of ways (most obviously, it imports and exposes os, so if for some bizarre reason you want to avoid importing os yourself, you can simply run "mimetools.os.popen" directly); no competent programmer would expect otherwise.
The second "flaw" is that pydoc runs a pager program which lets you run an arbitrary command if you control the program environment. Of course, the documentation states explicitly that the specified pager program will be used. It's unclear what part of the behavior here he thinks even surprising. And, again, the pydoc module imports and exposes "os" in exactly the same way that mimetools does.