I see this occasionally with small companies, usually it's more of a personal request from one of the employees to provide some code on a volunteer basis, perhaps solely because they are passionate about that sort of thing and someone knew that about them.

In the end, if the favor is upheld and they provide the code/binary/whatever to the company (who has a contract to deliver such code), then that company's upstream contract is still fulfilled, technically it doesn't matter that the coder was not an employee or contractor. The only real downside I see for this is legal liability for the company if they end up unable to provide for their customer, but that's between the two of them and their contract, the coder is basically not on the hook for any problems.