(Tasty, but not the texture I was going for...) What may have caused this? Did I over cook? Is it possible the pork shoulder had too much (or not...

Hi Laura, I've had similar results before (though the cubes fell apart first, turning into tasty but hard little shreds) and it's so disappointing! Sorry about that.

I'm guessing they may have been frying a bit too vigorously toward the end. I've had the best results keeping them at a low simmer, both in the boiling and frying stages. If your pork was too lean, that might have been an issue too.

Did it seem tender before hitting this stage?

I have not made the recipe but would venture a guess that maybe your roast didn't have enough fat. During the frying process was there a fair amount of fat in your pan? In the recipe she say's that if the roast is not fatty enough you have to add some lard. By doing that the meat will fry but stay moist, Pork shoulders are pretty fatty at least the ones I have gotten and there is usually more than enough fat that has rendered, maybe its possible your roast was trimmed a bit too much by the butcher.