There doesn't appear to be a common element like a ticket vendor so who knows how the Riverbend Music Center in Ohio website controller made the jump - but it looks like it may be a case of mistaken identity.

Riverbend <b>Festival</b> in Tennessee shows GPN as part of their line up 
http://www.riverbendfestival.com/pages/lineup 

Checked and is also on GPN's site now 
June 11, 2010	Riverbend Festival	Chattanooga, TN