Eyewitnesses + Engine noise
I'm not a pilot, but I know that sound travels at 340m/s (sea level)..
This means that for someone 1000m from the crash the sound and what he/she sees have a time diffirence of ~3 seconds...
With a vertical speed of 4000ft/min, 3 seconds is 200ft. Somenone reporting that he heard the engines 'reving up when the plane hit the ground', then in reality the engines reved up at 200ft.
Have it in mind when you think about eyewitnesses reports, eye witnesses are not flight data recorders, and I doubt that the accident board will ask them to testify.
Add to that that planes sound diffirently depending on the angle that you are(a bit extreme comparison, but have you seen an A380 slow flyby? You can
barley hear it from some angles)