The lending disruptor could have lots of room to rise, but it might not be for the reason you think.Upstart (UPST 1.65%) has been an excellent performer in recent years, with the stock up by 168% over the past three years. And there are some good reasons it has done so well.Most significantly, Upstart's business has grown tremendously, even in a so-so environment for lending. In the second quarter, Upstart's loan origination volume soared by 154% year over year and revenue more than doubled. And not only wa ...