You don't sound a big believer in bw exercise if you refuse to believe someone can grow from them...
But wot reason do I have to lie? I'm not selling you a workout program or a supplement, am I? It doesn't effect me if you decide to do pistols or not.
I didn't even provide an objective measurement of my thighs - just suffice it to say that I had quite large thighs to begin with for an untrained guy, and they definitely got bigger to the point of being, I dunno - rugby forward player sized, for a person of my height when my only leg exercise was pistols - that is the truth. I'm not sure why you want confirmation!
It makes sense - if you progress from being able to do 3 reps of pistols in a set to 40 - some growth probably occurred to facilitate that.
Now I need to progress them, however, which is why I need to learn to do them with a neutral spine before I load them, and I'd still like videos of someone doing them ass to grass with a neutral spine if you've got any...?