Only if the strong type system is specified to return errors on those kinds of mismatches, as opposed to using the type information to perform a conversion and

Only if the strong type system is specified to return errors on those kinds of mismatches, as opposed to using the type information to perform a conversion and give another result which is just as well-defined as an error. That's the point: Strong typing ensures all results are well-defined, as the result of a specification, and it uses type information to do that. Weak typing throws away type information, so it can no longer uphold such specifications.