I've watched the Ind-Pak replay multiple times now
Firstly, DK received a high full toss and Kohli had already remonstrated about it, but since Karthik was down the pitch, no one cared. By then, Virat had planted this aspect in the umpires' minds.
Now this is something I only noticed during the replays - before the no-ball, you could again see Virat talking to the square-leg umpire and suggesting that he take note where he was standing because there could be a no-ball. He had predicted the possibility of the ball slipping out, with Nawaz trying to go yorker full. A sideon slomo of the ump shows him staring for a bit at Kohli's waist before turning to see what had happened at the boundary.
Kohli's match-awareness was genius. And that's all there was to it. He is on another level of being in the moment.
And yeah on topic, no harm in reminding the umpires of the laws in case they forget things in the heat of the moment. As long as he's not intimidating the umpires like Richards, Ponting and Dhoni have done, there's no issue here.