Here's video and pictures I found. I think it's definitely a penalty by the letter of the law, but I also give Donnarumma the benefit of the doubt on this play, as he was committing to the ball before Musiala was in a direct path between him and the ball. I also think Musiala has to do a better job of protecting himself there, as it almost feels like he was trying to shield off Donnarumma.
Just an unfortunate play.