Hello and welcome to HealingWell.
Only your Dr. can give the specific reason. IMHO, the nurse spoke out of place as it is the Dr. who will be reading and making the conclusion on the results of your stress test. I would wait to talk with him and not over think the nurses comments.
Many people have abnormal EKGs that are benign.
Take care and do let us know what the result are of your stress test.