This isn't how working physicists talk, though. The physics researchers who develop mathematical models for physics are called theorists.
A string hypothesis would imply that they've come up with anything that's actually testable.
I know people attempted to correct the definition of 'theory' to discredit the 'It's only a theory' argument, but claiming it's only called a theory when it's "proven" is an overcorrection. In fact no theories are "proven" per se, the better theories just have known limitations.
“A hypothesis is a tentative explanation that can be tested by further investigation. A theory is a well-supported explanation of observations. A scientific law is a statement that summarizes the relationship between variables.” - The Internet
I think we can safely dismiss 'The Internet' as an authority on anything.