I've no idea what the licensing agreement was before they sat down to write the code, but if it was as informal as the handshake-that-wasn't, I'm gonna put forward the following idea:
By default, code belongs to the author of that code. Unless another agreement is in place, Bobby owns his own contributions to that project.
With that thought, the potential outcomes of this become a little clearer.
If no contracts were signed, I wonder if that would be the default, anyways. If it were to go to court, the absence of a contract would signify that no change of ownership has occurred, and since the work was done for free, there would be no implicit agreement of work-for-hire. Therefore, deciding ownership would be a simple (ha!) matter of examining the commit logs.
I was in a business (music publishing) for a number of years that dealt heavily with copyright law, but IANAL, so I could be way off here.
By default, code belongs to the author of that code. Unless another agreement is in place, Bobby owns his own contributions to that project.
With that thought, the potential outcomes of this become a little clearer.