A rare day when I do not agree with Phil! I think this is an unsuccessful drop goal and is covered by the exception to 21.11 and is a 22 drop out.
Surely the exception only applies if the ball is kicked dead without touching anyone on the way? In this instance the ball was deliberately touched by a defender prior to crossing the goal line.
BALL KICKED DEAD THROUGH IN-GOAL
11. If a team kicks the ball through their opponents in-goal from the field of play
into touch-in-goal or on or over the dead-ball line, the defending team can
choose :
a. To have a drop-out anywhere on or behind the 22-metre line; or
b. To have a scrum at the place where the ball was kicked.
Exception : An unsuccessful kick at goal or attempted dropped goal. In these cases,
the defending team restarts with a 22-metre drop-out.