Many doctors call the same "thing" by different names? There are some doctors who don't accept the idea of an alter, and use ego state instead. (And there are some who use both descriptions.) Until an alter confronts the doctor in some way, and is documented as an alter (by any name) it might be called an ego state (because it can't meet the dx until the doctor is aware of a secondary personality, if there is one.)
I wouldn't worry about what or who it is, and am glad that your doctor stuck with you on the phone.