Right you are Bushie. I got my information from Walsh, of course. He published the 6 part series on the history of Tex-Mex in the Press in 2000 and the article you linked is one of those parts, altho it reads a little differently than I remember. It's also the basis of one of the chapters in the new Tex-Mex book by Walsh. There's a link to the 6 part series at the top of the link you posted: http://www.houstonpress.com/special/texmex.html
It's mostly about Houston (Walter Berryhill, Felix Tijuerina, etc.) but there's a lot about Austin too, so you might find it interesting if you haven't already read it. I like Walsh's writing. The Tex-Mex book is not as good as his BBQ book, IMO, but it's interesting. More history than recipes. I had a copy of the Diana Kennedy book within a year of it's publication but had no idea of the stir it was creating among Tex-Mex restaurantuers.
In the book he adds a little more about the Roundup restaurant, which I guess would be a roadfood classic if it were still in existence. It was a drive-in. People sat in their cars and drank beer and ate. Tila Garza originally started putting some fajita meat on the complimentary (!) botanas platters along with nachos, chalupas, guacamole and lettuce. It became very popular and as customers demanded more of it, she started charging for it and served it on a sizzling comal.
Here's something I can add to the lore of the launch of the fajita craze
. I don't know just when Ninfa opened her restaurant; I have read that in 1969, she and her husband were still operating a tortilla factory out of the place on Navigation and it was only after he died that she took the advice of friends and put some tables in the front room of the factory and started serving the foods she was known for cooking at home. The movie 'The Thief Who Came to Dinner' was filmed in Houston, probably in late '72, early '73, and released in '73 according to imdb.com. It starred Ryan O'Neal, Jacqueline Bisset, Warren Oates, Jill Clayburgh, Ned Beaty and others. While they were in town filming the local papers covered their every move. Somehow they got turned on to Ninfa's and went there to party frequently. That's how I, and most other Houstonians, first heard of Ninfa's. Whether she already was serving tacos al carbon, I don't know, but her restaurant became a 'destination' and I'd imagine the Hollywood types went back to the left coast and told friends about the new dishes, too.
Then there's the part of the story that has to do with Cosmopolitan Magazine and their first male centerfold issue featuring Burt Reynolds and what Ryan O'Neal had to say about it, but I'm tired of typing this morning