DRtg isn't an individual stat; it's a team stat (who you're on the court with).
Either way that still wouldn't be showing DJ in a good flavor as most of his time was guarding Williams. His defense should absolutely be better considering the contribution Williams made.
That last paragraph isn't true nor is it fair. As DRtg is a "team" stat it doesn't really mean anything individually as (unless I'm mistaken) the bench got beat just like the starters.
The only other defensive stat that comes to mind for individuals would be defensive PER. I don't know what it would be with DJ on Nelson...but vs, Williams he absolutely won that matchup as he had a PER of -0.8. I didn't even know a player could have a negative PER!
We know Nelson blistered Felton; he had a PER of 29.6 (WOW!).