For the average person, 120,000 miles would be the equivalent of 8 years. Same with vehicle warranty. I have to say that this may or may not be an error. Per Tesla's support page for the model S & X have 8 years. They put in parenthesis mention of the 60 kWh battery. which if i read correctly is 8 yrs or 125K miles. We'll have to wait and see.
Model S and Model X – 8 years (with the exception of the original 60 kWh battery manufactured before 2015, which is covered for a period of 8 years or 125,000 miles, whichever comes first).