The code to read from dbc includes a additional folder which is not mentioned in the instructions.
Code is here:
#ifdef _WIN32
std::string dbcPath = m_dataPath + std::to_string(SUPPORTED_CLIENT_BUILD) + std::string("\\");
#else
std::string dbcPath = m_dataPath + std::to_string(SUPPORTED_CLIENT_BUILD) + std::string("/");
#endif
Which means ./dbc/ fails, but ./5875/dbc works fine.