It's a standard attack on cars with keyless entry and works with quite some brands. The basic idea is to extend the radio signal from the fob - which often lies close to the entrance of a house - to the car. Meanwhile some manufactures fixed this in newer models. One way to do this is to measure the time the signal needs to travel between car/fob and the car will not open if that takes too long. A "fix" for older cars is to store the key in a "signal blocker" (similar to those used for RFID cards). Specific to (older) Teslas is a different type of attack, where the (quite weak) crypto key of the key can be calculated in seconds, with the same result. The Tesla specific fix for this was the introduction of a PIN, that has to be entered before the car will start

Random link with some more explanation:  https://policinginsight.com/news/defend-relay-attacks-keyless-entry-vehicles/