Pogue Mahone
Closet Gooner.
The Son decision was fine.
Foot to foot offsides are always quicker as the offside points are on the same plane. Once you have the offside line from the defender's foot you can see Son is onside. Whereas if it was being measured from a shoulder or something then they would have needed the 3D calculations, which takes more time.
In this case you that Son is onside almost immediately, so they don't need to do a full calibration as there's nothing else to consider. It's nothing new, it just doesn't happen all the time because different incidents don't allow it.
Even comparing “foot offsides” you would expect two lines. One for the attacker, one for the defender. They never showed a second line and - based on the still images we did see - this was a close call.