Not a native speaker either so I may be wrong in this assessment, but a physio is someone who also gives therapeutic massages when needed. Hence, rubbing shoulders.
Yes, "rubbing shoulders" is a coloquial term to mean that you are standing next to other/famous people - at a crowded party or lining up next to each other for a photo opportunity etc. Your shoulders tend to bump or rub against each other in those situations. This is my friends case, as his Facebook feed is full of pictures of him standing next to (rubbing shoulders with) famous actors & politicians etc.
@oneeyedpigeon cunningly made the connection between my friend being a physio (physiotherapist) whose main job is providing healing and relief from muscle pain usually by rubbing or applying pressure. (Computer programmers like me who spend a long time at the keyboard often visit a physio to get our shoulders manipulated and rubbed to relieve built up tension).
Or rather rubbing shoulders is usually used to describe networking, though if you are mingling with the great and the good/important or famous, hobnobbing may have been a better term.
