The project may have some bugs that prevent it to compile but most of the issues are related to the proper use of frameworks and technology. For example in Java you will need to know how to proper create a REST service with Spring, but that is common knowledge if you are applying for Chief Software Architect.
You will need to review the code as best as you can and make changes accordingly. Less
I was able to whiteboard an LRU cache implementation using hashtable and DLL. However the interviewer was arrogant and kept saying "this wouldn't work". When I explained with an example, he said "its not thread safe" and kept going into tangential topics. We ended with CAP theorem and options to make it thread safe. He made statements like "you never prepared for this interview, did you?" and "you guys are never ready for a good interview" when I turned back from the whiteboard. Overall very bad experience interviewing here, I highly recommend you not to answer recruiter calls from this company. They are unprofessional and arrogant. Less