He was, his passing in particular was shocking. He did a couple of his trademark last ditch blocks/tackled that are down to his speed but he was an obvious weak link in basically every KO game.
Perhaps they went with the stat that Maignan conceded 3 goals in 570 minutes (1 conceded goal in 190 minutes), while the other keepers had worse record than him in this regard: (Diogo Costa 1/170; Unai Simon 1/142; Neuer 1/120; Sommer 1/120; Pickford 1/115; Verbruggen 1/77; Donnarumma 1/72; Mamardashvili 1/45).
Only Jan Oblak had better stats (2 goals in 390 minutes, or 1/195), but his team was eliminated two rounds earlier than France, on penalties, with Oblak failing to save a single penalty.