To answer your question straight, yes, farriery can definitely cause/create thin soles. BUT couldn't blame the farrier with the info you've given. Does the farrier pare/rasp into his soles, for eg?
I'm rather curious, as a horse I know has been dealing with issues recently stemming from him being EXTREMELY thin-soled. He has only recently had any foot-soreness issues (recently as in the past month or so now) and is now in pads + Equipac as well as Farrier's Formula and he is getting sole paint and Reducine applied once a day.
Assuming the farrier hasn't directly caused it, thin soles usually take some time to develop - assuming he had thick soles at all. Unfortunately that he's only recently become sore doesn't necessarily mean he had good feet until now. There may have been gradual 'low grade' issues that just mounted up. & perhaps the harder work was the 'straw that broke the camel'. Good that he's padded. Good diet & nutrition(who knows, may be the cause) will also help. It will take a fair few months at least to see any changes from nutrition.
sure they had his hooves x-rayed, he was a pretty expensive horse and they covered all their bases when it came to pre-purchase exam, as
Unfortunately it's not something that's always noticed, or taken into account, thin soles, stretched feet, etc, etc being so common & often not understood.
So... if you would like a critique or advice on your horse's feet, more info, about diet, environment, etc & hoof pics (see link in signature) would be handy.