I have gone to many local restaurants where local ingredients are used and not mass-produced and seen the same attitude from friends, colleague or acquaintances in my life.
I also extensively worked in the kitchen, in fact it was my first career, and i can say the attitude was prevlevant there too.
I've worked with plenty of people from mexico itself that had less of that attitude since they could actually see the influence of different dishes and spices in both foods.
So I can pretty much guarantee from actual experience this attitude stems from the same attitude that other people have that leads them to say things like 'italy doesn't have pepperoni pizza' or 'french wine will always be better than nappa' etc. It stems from the same place.
I will concede there are probably people like you describe, but the issue the article describes and the issue I am talking about is seen quite a bit against 'tex-mex'.