Sounds delicious. Machaca traditionally was made from dried beef (beef jerky). Now it’s typically made from leftovers as you described. In restaurants it may be scrambled with eggs.
In southern AZ, you won’t find the word machaca in restaurants. Most Mexican restaurants there still serve carne seca, from dried beef. Many menus will even serve a carne seca soup, called casuela. It’s all delicious and has a very unique flavor.
There was a restaurant in downtown Tucson that had big racks of drying beef outside in their courtyard. It’s been a few years and I can’t remember the name.
When I lived there, down the street from my place was an old fashion meat market that would sell dried beef. Carne seca is usually ground, similar to that stuff that came in a tobacco tin when I was kid. I’d usually eat it plain before I had a chance to cook with it.
My mouth is watering now.