A lot of mistakes were made with this decision, the referee obviously should have looked at the video and conferred with his peers for some time. As always, the referee is just one interpretor of the rulebook on the pitch - with VAR they have several referees to come to the correct decision together. If there ever was a long discussion to be had, this was one of them. Just like Pickford on van Dijk, where the wrong decision was made still.
For me, this is not necessarily a foul from the defender under Law 12. After the shot is taken, a new situation arises and he is then in front of DCL - not able to know exactly where he is going. As such, DCL is at most obstructed, not fouled. One could also (laughably perhaps) claim DCL is the one fouling the defender in the back of the head due to this new sequence and his leap over him, but obviously difficult to interpret. Some mention the defender pulling his foot up, but that’s after DCL nudges him in the head. So if you want to call the foot, you have to call DCL’s contact first and it’s a free-kick for the defender. However, the obstruction happens first.... so who the hell knows.
I am sure this situation will be brought up during referee discussion forums/meetings - and I am also sure opinions will be divided, even with rulebook in hand. Not all situations are clear-cut.