No, defense has been terrible, they just got lucky four games in a row like hump says
Very specifically here are a couple who have gotten better:
Van Noy - has really impressed and continues to improve. I think with High out he is one that will step up as a leader on that D
Bademosi - Plays great man coverage, physical, he has impressed a lot in the last few games
--
Big picture, what I have seen is Scar stabilize the line and thus keep Brady upright, and the defense seems to 'communicate' / organize better, and execute better. A number of the big plays given up early in the season were clearly miscommunication / confusion plays - you don't see those now. Secondary has played great vs pass. LBs are improving vs the run. At this point in the season I want to see the offense improve. Their offense should be putting up 30+ per game and it's been stuck at 20 a game right now. Thankfully it coincided with the D stepping up, but to make a run the offense needs to be counted on for 30 vs most teams.