I don't think it fits the definition of intentional.
- It wasn't excessive contact.
- It wasn't a deliberate foul designed to stop the the clock.
- It wasn't contact designed to neutralized an opponents advantageous position.
It was merely an attempt to block the shot that failed. Just because it was with an illegal appendage doesn't make it an intentional foul when it contacts the arm instead of the ball.
On an unrelated angle...If the player, with that foot, had contacted the ball instead of the arm, would have you called a kicked ball and killed the shot?