Repectfully, no, you cannot charitably call Taco Bell 'Tex-Mex'. This is easy to remember, because Taco Bell is from Southern California, and Tex-Mex is from...

Repectfully, no, you cannot charitably call Taco Bell 'Tex-Mex'. This is easy to remember, because Taco Bell is from Southern California, and Tex-Mex is from... Texas. A cursory Google or Wikipedia search could clear up your misunderstanding, but if you really want to dig deeper into the topic, I strongly recommend Gustavo Arellano's Taco USA, which is a fine popular history of regional Mexican cuisines in the United States.