One working definition of "anxiety" amongst therapists is: "an over arousal of the autonomic nervous system". This over arousal can be caused by many things including: thoughts, emotions such as guilt, regret, shame, remorse, anger etc or some sort of imbalance within the brain of the individual. If anxiety is an over arousal of the autonomic nervous system then it is very much a physical disorder as well as a mental disorder. Even if anxiety were caused by thinking alone there would still be a physical, felt presence of anxiety within the body.
It makes sense to look at both mental and physical causes for anxiety. It makes sense to look at the treatment option of medication given the research backing up the use of such meds. People are not machines and we do need more focus on treating people as individual human beings rather than just telling them to pop a pill and acting as if that somehow automatically makes things better. But meds clearly have a place in treatment plans for anxiety disorders.