Where is the routing info derived from. Is it a just a db based on the the presented flight number? Or can it come the aircraft? Reason I ask is that I have a Belgian AF C130 on at the moment, Flight ID as BAF619 but shows the routing EGQL-EBBR (leuchars Brussels). So is this its actually routing or just some spurious info stored in a db?
The route displayed is from a table in NavData.db3, there is no provision in Mode S for aircraft to transmit route details.
However it won't come as any surprise to you that the Belgian Air Force doesn't fly regular scheduled services, so any association between a specific flight number (e.g. BAF619 in your case) and a particular route is pretty meaningless and I don't know why it's even in the database.
I've picked the BAF Airbuses with this callsign on numerous occasions, heading in lots of different directions.