I would say that it probably was an unlucky break, spoke chain, etc. It could be mechanic related, if it could have been prevented. Trek will probably say that there was nothing inherently wrong with the frame that could have caused this, unless you started out with some waked out bent derailed hanger that caused a shifting err, but that probably isn't likely because any competent mechanic would snuff that out. I don't see how Shimano could be liable. I think it's going to come down to either the bike shop or the Trek. Could be just bad luck, but things like this don't generally happen on new bikes. Sorry about your frame. Hope you can get Trek to replace it.