There's no going around it - it's an amateur mistake. I'll give him some benefit of the doubt because the pitch was horrible, everyone was sliding and falling left and right and ball probably behaved in an odd way.
If he had to make such a dumb mistake, then at least it's good that it was in the first CL game with stakes still relatively low. It rattled him badly, I doubt he will do it again.
The second Bologna goal is a collective cock up. We would never know whether Bastoni/Acerbi instructed something to Pavard and the latter didn't understand. Or if the defence has agreed they should switch in that situation. Still, I suspect Bastoni is the main culprit. He was on Zirkzee and he suddenly switched to the overlapping runner which ran to Pavard's zone.
At first I blamed Pavard, but after watching the replay it seems to me Bastoni is the culprit. He's with the striker, Pavard and Acerbi runs to cover the 2 Bologna players that entered our zone, then Bastoni suddenly leave his position to come to Pavard side, who try to block the shoot.
There were series of wrong decisions made in that play. Bastoni running to cover for Acerbi, leaving his guy alone. Acerbi AND Pavard reacts to that, both running to cover Bastoni's flank. Then Bastoni realizes Pavard's flank is free so he attemps to cover that (as Zirkzee is back towards our goal at that point). So at that point it's a free shot from the edge of the box. But what is Sommer doing? Did Pavard's block attempt deceived him this much? He didn't try to make the attempt, meaning it was way too late when he saw the ball or he was already doing some prediction in his head and it went the other way, so he was way too late again?
There's still something to be rehearsed with that back trio, you can't triple one guy and then scramble from there, it's gonna be a mess after that as the attacker didn't even do some fancy shit, apart from that first fake shot/pass attempt.