@santa sangria has it bang on.
Looked back at the replay on Iplayer. When the Ecuadorian attacker challenges the Qatari goalkeeper, the Qatari #16 becomes the last defender, and Qatari #1 becomes the second to last, putting the offside line on him.
At the point of this challenge, the Ecuadorian attacker, whose number I can't see, has his front foot offside. The ball then spills, with no other player touching it, until the Ecuadorian attacker comes back from his offside position and plays the ball.
I hope that makes sense...