Physics
Physics is a branch of Science. Science is the practical application of Logic (in the form of the Scientific Method) to expand knowledge. A Logical Argument requires evidence.
String "Theory" does not have any supporting evidence. It is not based on fact nor reality. It is nothing more than conjecture.
As such, String "Theory" does not follow the Scientific Method. It is not a valid Scientific Hypothesis, let alone a Scientific Theory. It is not Science, it is not Physics.
Philosophy
Philosophy is the study of life's problems through Logic and Reason. A Logical Argument requires evidence.
String "Theory" does not have any supporting evidence. It is not based on fact nor reality. It is nothing more than conjecture.
As such, it is not a valid Logical Argument, it is a Logical Fallacy. It is not a topic for reasoned debate or inquiry.
tl;dr:
String "Theory" has no evidence. That makes it fallacious and irrational. It is NEITHER Science nor Philosophy.