We had this debate before and unless the devs from FV went to Lukes House, started up his PC and downloaded the Banished C++ Source code on a stick it seems very unlikely they have the source code stolen for Banished.
They took a lot of ideas from Banished and copied maybe some Icons and layout and UI stuff but I am quite certain they not have Reverse Engineered the Banished Source Code.
To complete reverse engineer compiled source code is a major pain in the butt if even possible at all. It is faster and easier to just write the code yourself. What you get if you load Luke's code into for example OllyDB is a bunch of Memory Addresses and Assembly code.