There is no double minor for elbowing. Minor or major.
According to NHL rules, double minor penalties are only assessed for butt-ending, head-butting, high-sticking and spearing, although a major penalty must be imposed for an elbow resulting in an injury to the face or head of an opponent (which would also result in a game misconduct penalty)
So the NHL officials determined that Carlo was not injured on the play
NATIONAL HOCKEY LEAGUE OFFICIAL RULES 2019-2020
TABLE 4
(Rule 18 – Double-minor Penalties)
SUMMARY OF DOUBLE-MINOR PENALTIES
Description Rule
(i)Butt-ending - Rule 58
(ii)Head-butting - Rule 47
(iii)High-sticking – Rule 60
(iv)Spearing - Rule 62
SECTION 6–PHYSICAL FOULS
Rule 45 - Elbowing
45.1
Elbowing - Elbowing shall mean the use of an extended elbow in a manner that may or may not cause injury.
45.2
Minor Penalty - The Referee, at his discretion, may assess a minor penalty, based on the degree of violence, to a player guilty of elbowing an opponent.
45.3
Major Penalty - A major penalty, at the discretion of the Referee, shall be imposed on any player who uses his elbow to foul an opponent.
A major penalty must be imposed under this rule for a foul resulting in an injury to the face or head of an opponent (see 45.5)
45.4
Match Penalty - The Referee, at his discretion, may assess a match penalty if, in his judgment, the player attempted to or deliberately injured his opponent by elbowing.
45.5
Game Misconduct Penalty -
When a major penalty is imposed under this rule for a foul resulting in an injury to the face or head of an opponent, a game misconduct penalty shall also be imposed.