Since Google purchased Waze a little while ago, their traffic data has used input from Waze. This is irrespective of the phone OS on which the app is running.
Waze is not the only source of information, any app that can give Google positional - and thus speed - can add to the accuracy of the data.
The traffic information is derived from speed, not the number of phones in an area. Therefore, phones not running Android don't 'throw off' the data, they just don't add to it.