Dick said he thinks there are many possible explanations to fit the facts of phenomena.
The facts of phenomena are described by the laws of physics. That is, the laws of physics predict the behavior of phenomena within certain margins of error.
Explanations are something else again. Even Newton, after producing a pretty good predictive law for gravitation admitted that he had no explanation for how matter could produce such action at a distance.
You just remarked that even though QED is a remarkably accurate predictor of phenomena, we still have no explanation for why the facts are as they are.
So, we have one set of facts: That is the way we observe phenomena behave. That is the one given. We then go about trying to come up with theories which contain equations describing the behavior, and to some extent, an explanation which is some kind of understandable model making sense of the equations.
String theory has the model of these loops of string vibrating in multi-dimensional space. There is a huge variety of possiblities for the topology of the space and the configuration and behavior of the strings. String theory will be successful when it can point to at least one of those possibilities and show that it leads to equations that are equivalent to, and hopefully better than, the equations of QM, SR, GR, etc. They must be nearly equivalent or else they wouldn't "fit the facts" and the theory would be declared "wrong".
So, what I said, is that there is a possibility that one or more of the string theory models, or explanations, (I called them hypotheses) might lead to the known laws of physics i.e. "fit the facts", and that the rest of them cannot happen in reality.
I don't know if that helps or not. Let me know.