No.
The only OpenStreetMap based navigation app with live traffic data is Magic Earth. It’s not foss, but gratis.
They get the traffic data from some third party, not by following their users like gmaps. That is the reason live traffic is only available in just some countries: https://www.magicearth.com/feature-availablity/#hd_traffic
No. It means they get the data from somewhere else, maybe from some carsharing app, or from some government db from car counting thingies mounted on traffic lights, etc. There are other sources to get traffic data ftom, but usually following users is more convenient and reliable
They wont tell us where they get it from, they only say it’s not generated via this app. They are followimg someone, but not me.