I'm not sure exactly what it means when you lead the NFL in a stat during the preseason, probably that you played a lot... But it certainly can't be taken as a bad thing. Because while the games don't count, these are still are guys doing things against other guys trying to stop them. So it has to say something about your talent if you're tops in the league.
At the end of preseason, Eagles led the way in the following areas.
Passing TDs (individual) - Nick Foles tied for the league lead with 6.
Passing TDs (team) - Eagles led the NFC with 10
Total defense - Eagles led the NFL allowing 213.8 yards per game.
Passing yards allowed/game - Eagles led the NFL with 125
Rushing TDs - Tied for league with 0 allowed
Sacks - Led the league with 20 (2nd place had 17).
The Eagles were also one of only 2 teams in league to go undefeated in the preseason. Funny enough, 3 teams went winless and they were all in the AFC East. Overall, the Eagles defense was really the standout in preseason, even moreso than we realized. Now, will being the best preseason defense carry over into the regular season? That remains to be seen.