I think I know what you are talking about. It is a mix between distortion and dissonance. Distortion I'm sure you are aware of already. Even if they are playing clean, they sometimes use a little distortion behind it to make it sound a little "grindy".
Dissonance on the other hand is just an effect that multiple notes create by themselves. Think of it like an "imbalance" in sound. If you play two C's on the fretboard, there is no dissonance since the tones are exactly the same. Play a C and a C# (on another string of course) at the same time and you will hear a sort of "vibration" effect.
You'll notice this a lot when tuning up. If you use the 5th fret to the next open string method to tune you can play with it and see. Strike the 5th fret and then tune the next string UP to that pitch. The closer you get, the faster the "vibrations" go. You'll hear it. Once the two are in perfect pitch with each other, you'll get a smooth sound. That's why you'll hear a lot of people tune by hitting two notes and then tuning UP to that pitch.
Alright....so how does this relate to your question? When they are doing those bends, they aren't just playing 1 string. They are bending a note and also holding a different note on another string.
-Hold the 12th fret on the 2nd string with your first finger. Put your third finger on the 3rd string, 14th fret. Hit both at the same time, but bend the note on the 14th fret.
It'll give it a unique sound and when you look at the theory behind it, you are playing a Major 2nd interval (I'm pretty sure. Someone correct me if I'm wrong). The 14th fret is A, the 12th fret is B.
The dissonance, along with the fact that you are playing two different notes, gives it a unique sound. Add some distortion to that kind of bend and I think that is the sound you are working at. Actually, that chord shape is pretty common (Note X, then 1 string up 2 frets over). Even without bending. Just play that and slide it up a couple frets. Throw it in the mix when you are playing single notes and you'll hear the difference.Edit
: That reply was longer than I thought. Also realized I may not have answered your next reply. You asked if that sound was all from distortion. What were you referring to? Your original question, or pinch harmonics?