Hi,
That's normal. The "use bootstrap design" setting of the HikaShop configuration, which allows HikaShop to be responsive, is apparently turned off on your website. Thus, HikaShop doesn't adapt the display to the small resolutions.
Turning on that option would allow for that, but it requires your Joomla template to include bootstrap, which is doesn't as far as I can see on your website. So you would also have to add it to your template. Here is a tutorial about that:
www.inmotionhosting.com/support/edu/joom...mplate/add-bootstrap