Freebie from developers or by accident | Distance sensor reading accurately without a sensor!

F.C CUBE ORANGE
PX4 v1.13.3

Hi,

i find it very intreating that while there is no distance sensor connected on my Quadcopter . However i am getting very accurate distance sensor plot about my altitude when compared with the graphs from GPS , barometer and fused data . Is that a coincidence !

Log file https://review.px4.io/plot_app?log=ccb6b5f2-2aee-4f1b-8bd3-79282ebcd233

Any alien out there who could explain this wonderful freebie function, would be great

thank you