A statement like this in a pension application is a claim, not proof.

Bourland's Texas Cavalry organized a year after smoke from this battle had cleared. Williams could have belonged to another Texas command involved in the Battle of Elkhorn Tavern, March 7-8, 1862, possibly the 11th Texas Cavalry. A man named Thomas Williams is carried on roll at the end of 1861.

Here's an image of the Texas memorial at Elkhorn Tavern naming each command involved --
http://www.waymarking.com/gallery/image.aspx?f=1&guid=286493b8-8453-426c-ab56-048fc4d9eb7e&gid=3

http://www.civilwarhome.com/pearidge.htm