Dale Johnson from ESPN, who always seems to have insider information from PGMOL, said that Michael Oliver sent Andy Madley to the screen for a potential penalty but also told him there was a potential foul by an attacker in the build up. So Madley agreed it was a penalty but then decided there was a foul in the build up so gave a defensive free kick. Makes sense if you think about it, if the VAR can only recommend a review for a penalty for the referee to make the final decision, the same should happen for a potential foul in the build up as they are both subjective decisions.