It doesn't have to be personnel-wise. They played a weak NFCE, and they were coming off a previous 4th place finish which means they played 2 other 4th place finishing teams.
- Inside the NFCE, they allowed 15.5 points/game. Outside the NFCE, they allowed 23.6 points/game
- Inside the NFCE, they scored 25.3 points/game. Outside the NFCE, they scored 18.3 points/game
- Inside the NFCE, they allowed 243 yards/game. Outside the NFCE, they allowed 341 yards/game
- Inside the NFCE, they generated 10 turnovers. Outside the NFCE, they generated 13 turnovers
- Inside the NFCE, they had 10 turnovers. Outside the NFCE they had 17 turnovers. +/-0 within the division, and -4 outside the division
- Inside the NFCE, they held the ball for 31:35/game. Outside the NFCE, they held the ball for 28:54/game
Absent a repeat from last year in terms of the NFCE's suckiness, I don't see how they'll match last year's production. Assuming Dallas is better from having Dak back and Philly is better from not having to fool around with Wentz, Washington already has 6 tougher games on their schedule than they did last year. 4 between Dallas and Philly, and 2 random other 1st place division winners instead of 4th place division losers.
I don't think their defense is bad, but I do think they benefitted from playing against an awful NFCE. If the rest of their schedule had performed like the NFCE, they would have been the league's best scoring defense by 3 points/game. If the NFCE would have performed like their opponents in their other 10 games, they would have been the 17th best scoring defense. I don't blame them, they can only play who is on their schedule, but when 6 of 16 games are against absolute trash, the numbers can really start to look really good without meaning a whole lot.
Their defense will be top half of the league - likely in the low-teens - but I have a hard time believing they will be 4th in scoring and 2nd in yardage again.