Maguire was asking for the ball though, watch him closely, he is signaling for the ball.
It could be argued that De Gea should have seen the danger and passed it out wide to the full back, the one Maguire tried to lay the ball off to and failed.
De Gea and Maguire are both culpable in that situation. Maguire for not having the spacial awareness and threat around him and De Gea for also not recognising that a pass to Maguire, who though asking for it, was a hospital pass.
You cannot count out Tent Peg for that error as well, he must be telling them and coaching them to play out from the back, not matter what. A few years ago De Gea would have hoyed that up field. De Gea is not a goalkeeper who can play the "sweeper keeper" role, just look at his miserable attempt to bring the ball under control that lead to the 3rd goal.