When someone publishes code and says something like "solved <problem> in <n lines> of <pick your language>" there generally is an implied "my language is better than yours" subliminal message that, for some strange reason, is based on line count.
Let's not debate the merit of line count as a measure of how good a language may or may not be. If we are going to go there I'll write the same solution in APL and we'll start counting characters instead. Again, line or character count, in my opinion, is not a measure of the "superiority" of a language.
The 28 line solution is not pure Python. How do we define pure Python. Let's just say that "solved <problem> in <n lines> of Python" to me means that you download and install Python:
http://www.python.org/download/releases/2.7.3/
Install nothing else whatsoever and write code that solves <problem>.
OpenCV, which is what the author used for a couple of aspects of this code, is an extensive (and really cool) C++ library that is being accessed from Python. Here's the source:
https://github.com/Itseez/opencv
I'll leave it up to the reader to find the source for the Sobel method.
A much more honest title could have included something like "solving <problem> with <n> lines of Python using OpenCV".
As I said before, the intent of the article and what is being demonstrated are good, no, great. I just wish the title was a little more reflective of reality. That's all. No need to get worked-up. This is not that serious of an issue. Just a comment.