The Red Devils qualified for the last eight of the competition after securing a 3-1 victory at the Parc des Princes on March 6, overturning a 2-0 first-leg deficit.
Thomas Tuchel's men put themselves in a great position to progress to the quarter-finals after winning at Old Trafford, but they were undone in shocking fashion in front of their own fans.
Marcus Rashford grabbed the decisive winner in stoppage time at the end of the game, firing home from the penalty spot after Presnel Kimpembe was controversially judged to have handled the ball in the area.
PSG's season has already been dubbed as a failure in the wake of that result, despite the fact that there are still two months of the campaign to be played and two trophies still up for grabs.
Halilhodzic believes the Parisians got what they deserved, after failing to adequately prepare for the crucial showdown in the hours before kick-off.
Reports in France have claimed that instead of arriving at the Parc des Princes together on a team bus, the players made their own way to the stadium.
"The behaviour of the team before the match was incomprehensible," Halilhodzic told Le Parisien ahead of Nantes' trip to Paris in the French Cup semi-finals on Wednesday. "How they could accept that the players arrived alone to the stadium two hours before the match?
"The preparation of Paris before the Manchester United game was a serious mistake. It's unworthy for a big club. It's unprofessional.
"In Paris, there may be traffic jams or an accident [that would delay the arrival to the stadium]. The main lesson is: 'You acted like a child, so you have the result of a child'."
PSG have never won the Champions League and they have only managed to appear in the semi-finals of the competition once - way back in the 1994-95 season.
Since they received financial backing from billionaire Qatari investors in 2011, they have only managed to arrive in the quarter-finals once, suffering several damaging defeats against the likes of Barcelona, Real Madrid and Chelsea.
Tuchel's side looked well poised to end that hoodoo this time around, which made the United defeat even tougher to bear for supporters around France.
Instead, PSG have been left chasing another domestic double, with a 20-point lead to protect in Ligue 1 and a French Cup final to aim for in May.