Philosophy touches many different fields and it seems quite natural to me that interested people explore the border regions. If you are a physicist or even if you are only interested in physics it is quite easy to recognize that there is a problem with the idea of free will. Or if you are a neurobiologist. Mathematicians naturally get into contact with logic, proofs, knowledge and the like. Or think of linguists. Not that any of them would be a full-fledged philosopher but there are for sure areas of philosophy where people from other professions naturally have something to say.