Ref's probably got it wrong.
Rule 6-1-2 provides:
Free Kick Formation
ARTICLE 2. A ball from a free kick formation must be kicked legally and from some point on Team A’s restraining line (Exception: Rule 6-1-2-d# and on or between the inbounds lines. The referee will declare the ball ready for play when the officials are in position after the kicker has received the ball. After the ball is ready for play and for any reason falls from the tee, Team A shall not kick the ball and the official shall sound his whistle immediately.
When the ball is kicked:
a. Each Team A player, except the holder and kicker of a place kick, must be behind the ball
b. All Team A players must be inbounds.
c. At least four Team A players must be on each side of the kicker
d. After a safety, when a punt or drop kick is used, the ball may be kicked from behind the kicking team’s restraining line. If a yardage penalty for a live-ball foul is enforced from the previous spot, administration is from the 20-yard line, unless the kicking team’s restraining line has been relocated by a previous penalty.
e. All players of Team A must have been between the nine-yard marks after the ready-for-play signal
For any free kick formation, the kicking team’s restraining line shall be the yard line through the most forward point from which the ball shall be kicked, and the receiving team’s restraining line shall be the yard line 10 yards beyond that point. Unless relocated by a penalty, the kicking team’s restraining line on a kickoff shall be its 30-yard line, and for a free kick after a safety, its 20-yard line.
On a long kick off we don't want to split hairs and be too technical of calling whether there is an encroachment foul [off side] by the Kickers. There will times when one of the players beats the kick by an inch or a half step. We tend not to call these unless it is a continuous problem or unless the kicking team player's body is fully across the restraining line. Again officials are liberal with their enforcement on a long deep kick off because rarely is there an advantage gained. A player whose entire body is across the line or is taking a step beyond the line creates an unfair advantage and that is called a foul. There is also a practical reason - being too technical could cause delays and multiple kick-offs with multiple fouls and truly serve no just purpose. It could also take momentum from a team. Conversely, on an on-side kick or short kick officials are very strict and enforce the restraining line restriction. But bear in mind, the kicker and Holder are permitted to be on or beyond the restraining line.