Did he just order and take delivery of this car in the past couple of months? For a short time earlier this year, they offered Standard Range Model S and Model X which were battery limited to 92% of the 100kWh battery and cost $8000 less. 335 miles*0.92 = 308 miles for the S, pretty close to the observed 310 miles your neighbor is getting. Before any were delivered, they eliminated the Standard Range option for the X but kept the Standard Range S around a couple additional weeks. Sounds like he might have received the Standard Range S. They don't have new badges yet so they put the 75 badge. Our new Standard Range X was updated before delivery to be Long Range and has the 100D badge even though it shows as Long Range online. Does his show as Standard Range?
If he checks his battery, he will probably see the part number is for a 100 kWh battery. Option code should be BTX6.