My feeling is that if ever you are contacted you insist very firmly that the accident had absolutely nothing to do with you. At the moment it occured you were not in your car which was legally(?) parked and locked. Neither were you on the carriageway and not in the path of the cars. If I understood correctly you were actually on the footpath at the time of the accident(?). That you suffered no damage and that you only gave your details, out of the goodness of your heart, in case either party required a witness.
Express extreem puzzlement as to why the accident occured and other than that limit yourself to describing what you actually heard.