Or an alternative explanation, it just simply implemented the long standing functionality that (often rapidly) slows the car to the speed of an adjacent slow moving lane to prevent speeding past a lane where someone may suddenly pull out from. It indicates this behaviour by showing chevrons and any alignment with a gap in traffic was purely coincidental.
That functionality has been around for over 3 years and nothing to do with FSD beta.
If you're in the left lane you're going to Manchester. If you're not, you're not. We were in lane 2 and the car knew we needed to go left.