Here's what's happening: Blogger mobile templates don’t currently support widgets, so the Disqus widget doesn’t replace Blogger’s default comments system when your site is viewed via a mobile device. Essentially, when people view your site using a mobile device their comments bypass Disqus and are posted straight to Blogger .
Until Blogger mobile templates do support widgets, you can fix this by either:
Disabling Blogger mobile templates; or
Disabling commenting in Blogger — this will not disable Disqus comments, it will only disable commenting on your mobile template; or
Manually enable Disqus in Blogger mobile templates (see below).
How to manually enable Disqus in Blogger mobile templates
Note: This requires manually editing your Blogger template and HTML. This is meant for advanced Blogger template developers only. We also recommend backing up your template first.
In Blogger visit your site's settings > Template.
Choose "Edit HTML".
Enable the "Expand Widget Templates" checkbox.
Search for "disqus".
Add mobile='yes' to the following: <b:widget id='HTML2' locked='false' title='Disqus for The Disqus Blog' type='HTML'>
Choose "Save template".
The result should look like: