How do power tailgate lifts work?

In the parking lot this morning I saw a tailgate on a GMC Yukon open up automatically. There was no one around the vehicle or in it. It stayed open for less than a minute then closed down again. The only other thing that could have been related to it was someone getting into their car about six parking spaces down. They used an auto-unlock on their keychain as they approached their vehicle. Their lights flashed and it went “beep…beep”. They got in and drove off. It was during this time that the unattended Yukon tailgate did its’ thing.
I assume it is possible that two different vehicles use the same frequency for similar operations but how common or uncommon would this be?