Your page is missing the following meta tag:
<meta name="viewport" content="width=device-width, initial-scale=1.0">
Add it after the opening <head> tag of your page.
Thank you, that was it. Although it seems rather odd that DW's template doesn't include this rather crucial bit to actually make it work.
Yes, that is odd. If it's "responsive" it most certainly should contain the viewport meta tag as do Fluid Grid Layouts and Bootstrap. I think you discovered a minor bug that should be reported to the DW Team.
You can add it to the file at...
Program Files > Adobe > Adobe Dreamweaver CC 2015 > configuration > BuiltIn > Responsive Starters > About Page.html
1. Open the file in your editor of choice and add the <meta>
2. Save As to your desktop (use the same name).
3. If you have full admin rights, drag it to the location above to replace the original.
As always, make a backup.