Like some other goals we've conceded, you can't say it's Maguire's fault, but it's reasonable to expect him to do better given his reputation and price tag, and we need him to do much better than just not making direct errors if we want to achieve higher. I've played as a defender myself and I've seen plenty of good defenders slide the ball away at the near post while having the cutback covered on similar occassions.
Here he marked the opponent's striker and successfully neutralized one threat, basic job well done. But then, as a quality defender, he had to at least make an attempt to cut off the second or third options from the attacker, yet he didn't even look at the ball and realize the ball had already been knocked past him. It seemed he lacked the awareness and athleticism to me.
For a top team doing the basic job isn't good enough, you expect your star players, especially the captain, to step up and do something extra to the team. Bruno is demonstrating that up front; Pogba, Rashford and Martial are capable occassionally; but neither our allegedly most expensive defender and highest paid goalkeeper are doing that at the back.