Chardet detects no encoding

Question

I want some data from a website with the following url: http://www.iex.nl/Ajax/ChartData/interday.ashx?id=360113249&callback=ChartData

I think the data is Json. Going to the url in my browser, I can read the data.

In python I have the following code:

import urllib
import re
import json
import chardet
url = "http://www.iex.nl/Ajax/ChartData/interday.ashx?id=360113249&callback=ChartData"
htmlfile = urllib.urlopen(url).read()
chardet.detect(htmlfile)

This gives the following output: {'confidence': 0.0, 'encoding': None}

When I print htmlfile, it looks like it is 'utf8'.

What could be the reason for this output of chardet?