Yes they did need to score 2 goals because Barcelona scored 6!!! You didn't even watch the game
first of all i have a great imagination, i have been through this situation many times on football manager and we were talking about their mentality during the main portion of game
tell me at what part of the game did PSG think they need a goal?
kickoff 0-0 (0-4) mentality: ok ffs just dont concede 4 goals
3' 1-0 (1-4) mentality: oh shit thats not good, lets just get over this and try to not concede for 15 minutes then work from there
20' 1-0 (1-4) mentality: ok now we are in the game, lets continue to defend
40' 2-0 (2-4) mentality: oh shit, ok lets just get to halftime without conceding a goal and regroup
halftime 2-0 (2-4) mentality: now this is looking tight, we have to work really hard in defence for the next 15-20 minutes, if they dont score then they will be increasingly open and we can hit them on the counter attack
50' 3-0 (3-4) mentality: oh shit now we are in trouble, we might need to score a goal now but at the very least lets not concede another
62 3-1 (3-5) mentality: hahahaha yes, ok now we got the goal, lets just sit back now and not concede anything untill the end of the game
85 3-1 (3-5) mentality: lol great job we are heading to the next round baby, just see this out
88 4-1 (4-5) mentality: ok consolation goal, lets just not concede another one, kill the game off
90+1 5-1 (5-5) mentality: ffs this is bullshit, ok just a few minutes, all hands on defece
90+5 6-1 (6-5) mentality: ffs what happened, ok now we need to score, oh shit theres the final whistle
so maybe for 12 minutes they felt they needed a goal, that ended as soon as they got it
yes its an invitation for barca to pile on pressure but its even more of an invitation to barca if they have to beat 5 or 6 and not 9 players, just ask italian teams who are the masters of defending a 1-0 lead how many world cups and champion leagues they have won