The content of the file in question is included in the returned data. You are getting the full GitHub view of that file, not just the contents.

If you want to download just the file, you need to use the Raw link at the top of the page, which will be (for your example):

https://raw.githubusercontent.com/someguy/brilliant/master/somefile.txt

Note the change in domain name, and the blob/ part of the path is gone.

To demonstrate this with the requests GitHub repository itself:

>>> import requests
>>> r = requests.get('https://github.com/kennethreitz/requests/blob/master/README.rst')
>>> 'Requests:' in r.text
True
>>> r.headers['Content-Type']
'text/html; charset=utf-8'
>>> r = requests.get('https://raw.githubusercontent.com/kennethreitz/requests/master/README.rst')
>>> 'Requests:' in r.text
True
>>> r.headers['Content-Type']
'text/plain; charset=utf-8'
>>> print r.text
Requests: HTTP for Humans
=========================


.. image:: https://travis-ci.org/kennethreitz/requests.png?branch=master
[... etc. ...]