There was initial confusion on 50 minutes when referee Tobias Stieler's whistle stopped Villa goalkeeper Emiliano Martinez from taking a goal-kick.
The confusion only grew when he pointed towards the penalty spot - until the television replays showed what defender Mings had just done - as a video assistant referee (VAR) check confirmed the decision.
Martinez had tapped a goal-kick to Mings inside the penalty area but the former Ipswich defender simply picked the ball up.
Mings had clearly not realised the kick had already been taken and that the ball was in play. He was penalised for his error and Hans Vanaken stepped up to fire home what turned out to be the winner from the penalty spot.
It is not the first time the Champions League has seen such an incident but Arsenal escaped being punished against Bayern Munich in last season's quarter-final first-leg.
In an almost identical incident, defender Gabriel handled a pass from David Raya inside the penalty area - again not realising his keeper had taken the goal-kick and that the ball was in play.
But the Gunners were allowed to take the kick again. Then Bayern manager Thomas Tuchel reacted furiously and said the referee had told his players he didn't award the penalty because it was "a kid's mistake".