yeah, but that's not all there is to the rule, iirc - regarding the defender, any part of his body counts with which he can defend/prevent a goal, which his feet obviously are and it's his trailing foot that seems very much in line with Mandzukic' head/body.
A player is in an offside position if:
He is nearer to his opponents’ goal line than both the
ball and the second last opponent.
IFAB Decision 1:
Consideration should be given to any part of the head,
body or feet of the attacker in relation to the second
last defender,the ball or the halfway line .
For the purposes of this decision, the arms are not
considered to be part of the body
Active Play
“Gaining an advantage by being in that position”
means:
Playing a ball that rebounds to him off a post or
crossbar, having previously been in an offside position.
Playing a ball, that rebounds to him off an opponent,
having previously been in an offside position.
This happened, clear offside