but it appears that the QC player never fully "tagged up"
It looks like the rule says touch the line
From the rule book
86.1 Offside - Players of an attacking team must not precede the puck into the
attacking zone.
A player is offside when both skates are completely over the outer edge of
the blue line involved in the play at the instant the puck completely crosses
the outer edge of that line.
The position of the player’s skates and not that of the stick shall be the
determining factor in all instances deciding an offside.
A player is onside when either of the skates is in contact with or on the
player’s own side of the line at the instant the puck completely crosses the
outer edge of that line. A player in full control of the puck who crosses the
blue line ahead of the puck shall not be considered offside.
While the position of the player’s skates is what determines whether a
player is offside, the question of offside never arises until the puck completely
has crossed the outer edge of the line.
If a player legally carries or passes the puck back into his or her own
defending zone while a player of the opposing team is in that defending
zone, the offside shall be ignored and play permitted to continue.
If the puck is intercepted cleanly by a member of the defending team and
is carried or passed by the player’s team into the neutral zone, the offside shall
be ignored and play permitted to continue, even if a member of the attacking
team has preceded the puck into the attacking zone. (Officials shall carry out
this rule by means of the slow whistle.)
86.2 Delayed Offside - If an attacking player precedes the puck, which is shot,
passed or deflected into the attacking zone, but a defending player is able
to play the puck, the official shall signal a delayed offside.
SECTION 10 / Game Flow 73
The official shall drop the arm to nullify the offside violation and allow
play to continue if:
1. The defending team passes or carries the puck into the neutral zone;
or
2. All attacking players in the attacking zone clear the zone by making
skate contact with the attacking blue line.
If the attacking team does not clear the attacking zone, the official shall
stop play for the offside violation if any attacking player touches the puck,
or attempts to gain possession of a loose puck while the puck is still in the
attacking zone, or forces the defending puck carrier farther back into the
attacking zone.
The attacking zone must be completely clear of attacking players before
a delayed offside can be nullified with the puck still in the attacking zone.
Whenever a defensive player gains possession of the puck on a delayed
offside, play should not be stopped when that player has a clear opening for
advancing the puck.
If a puck is shot on goal during a delayed offside, the play shall be allowed
to continue under the normal clearing the zone rules. Should the puck enter
the defending team’s goal during a delayed offside, either directly or off the
goalkeeper, a player or an on-ice official, the goal shall be disallowed. The
fact that the attacking team may have cleared the zone prior to the puck
entering the goal has no bearing on this ruling.
The only way an attacking team can score a goal on a delayed offside
situation is if the defending team shoots or puts the puck into their own net
without action or contact by the offending team.