Here is ESPNcricinfo's commentary of the call:
9.1 83.0 kph, lbw first ball. Long long chat, and they decide to review. Warner doesn't look convinced, but he has reviewed it. Warner has picked a ball too full to sweep and is beaten. The question is, has he got an edge or has it straightened enough? This is pitched outside off, the ball has straightened, and I don't see any part of ball in line. However, the machine is showing "umpire's call". I don't know how. I must be wrong, but I will need an explanation from somebody here. Don't see any part of ball in line. They show umpire's call. Both on impact and the stumps. On many more replays, perhaps one mm of the ball hit him in line. Oof 42/2
Australia ended up losing that review, and that quite possibly cost them later on; they would likely have challenged a Shaun Marsh lbw call if they had both their reviews in hand, and, as replays showed, Marsh would have been allowed to bat on.
Australia's official Twitter handle tweeted an image of the Hawk-Eye projection of the Warner dismissal.
— cricket.com.au (@CricketAus) March 7, 2017
In that image, to the naked eye, there seems daylight between the point of impact and the line of the stumps. The ESPNcricinfo commentary said in relation to the image:
Make your own minds if this was "umpire's call". My naked eye sees nothing, but I also know once you agree to use a machine you have to agree with it.
The machine has now explained how it returned an umpire's call. ESPNcricinfo has seen a Hawk-Eye video that removes the batsman from the image, and zooms in on the point of the impact from the top, as they do in tennis. That shows 2mm of the ball in line with the stumps.
"Although it may have appeared on first glance that the impact was slightly outside the line of off stump, in fact there was actually 2mm of the ball inside the outside edge of off stump, thus making the impact 'umpire's call', resulting in the original decision of out remaining," Hawk-Eye said.
It was unfortunate for Warner and Australia that they were done in by such a minute margin, but it was not inaccurate.