But that's the very definition of an ongoing foul. That's why you take the entire foul into consideration and not just the initial contact. If his shirt hadn't been tugged the attacker would have been well inside the box already.
Uefa have been actively encouraging their referees for years to enforce the rule properly because they want to minimise the use of tactical fouling on the field. Otherwise a defender who's lagging behind could bring down an attacker with a sliding challenge just before he reaches the box as a sort of damage control. The red card will be given anyway for denying an obvious goalscoring opportunity but he figures that at least it won't be a penalty.
The idea, of course, is to not have the player committing such a foul at all. Which is pretty sound. When it costs too much it's better to just leave it up the keeper and, if you concede, try to deal with it with eleven men still on the pitch.
