By default, the GSA sends a user agent value of "gsa-crawler".
Presumably, the (probably poorly-designed) site you're crawling looks
for common desktop browsers and assumes anything else is mobile.
You can change the GSA's user agent value to that of a desktop browser
to avoid this problem. This is set under Crawl and Index ... HTTP
Headers.
As an aside, it is my understanding that if you use the GSA to crawl a
public site, you need permission from the owner of that site to do so,
according to the product license.
Dave Watts, CTO, Fig Leaf Software
http://www.figleaf.com/
http://training.figleaf.com/
Fig Leaf Software is a Veteran-Owned Small Business (VOSB) on
GSA Schedule, and provides the highest caliber vendor-authorized
instruction at our training centers, online, or onsite.