This isn't a very rigorous test, and TC's assertion that this may be random is probably untrue given that the results seem to be consistent if you enter the same details multiple times. The idea that Equifax has implemented a random yet deterministic checking system seems beyond the pail of belief.

If I had to guess, I would say that Equifax is not checking against a list of people that they know are compromised, but rather against a list that they know have NOT been compromised. So if you check a name, and it is in Equifax's database AND it is known to be uncompromised, you get back a "you are safe message". For everyone else they give a generic "you maybe were effected", emphasis on the "maybe".

Obviously a fictional person with fictional details is not going to be in Equifax's database, so they would just throw the generic maybe message.