What does a call to go back to the surgeon mean? I had a lumpectomy?

Routine. Following any operation, it is important to see your surgeon within 1-2 weeks to be certain there were no postoperative complications. Furthermore, it is important to discuss what was found at surgery and what the next steps might be.
Get results. Most physicians these days will have patients come back in to go over results. It is more effective to provide results face to face and answer questions. If biopsy results indicate further evaluation is needed, then going over this info face to face is desirable.