Core is the rebranded business banking group. They are responsible for commercial banking relationships in the $5MM - $50MM company revenue range. This is changing as Wells is shifting to a more centralized model. There are other threads on here that beat this horse to death.
The do have clients with large real estate portfolios so maybe that's where the confusion with CRE came from. To be honest, there's a lot of gray areas when it comes to Core/MMB customers and customers of partner groups