Honestly, I think it's a tough one and not at all black and white. If Tielemans is in the process of taking a stride, and not shooting the ball, we'd say that Werner stuck his foot in front of him and tripped him. Since Tielemans is in the process of shooting the ball, Werner just nipping in and putting his foot between the shooting leg and the ball could be construed as obstructing the shot since he's never in control of the ball.
If that's a penalty, then any player can put his foot in front of the ball as a defender's attempting to clear it and buy a penalty. There are arguments for both sides, because the end result is obviously that one player gets absolutely twatted in the leg and ends up conceding a free kick, but has he put himself in danger (similarly to lowering your head) by just placing his foot between a shot/clearance and the ball? And if that's a penalty, then how do you judge a situation where a player trips another? Does the foul go to the one who makes the trip because he's the one getting kicked?