The problem on ASP.NET GridView control is that once it is rendered on a browser, it is automatically wrap by a "<div></div>" tag and the header is on the tables "<tbody></tbody>"
which contradicts to BootStrap tables methodology of using "<thead></thead>".
To fix the problem. Apply or add this small script below. What it does is transfer the first element and create "<thead></thead>" tag automatically. I am not a jQuery expert so please forgive my code, hehehe.
The very important one is to add the two classes on your gridView "grdViewTable" and "headerStyle"
Jquery Script
Fixed Tag Image: