"Distance by Elytra" statistic is approximately doubled

Can you give me a video/screenshot for this issue?

Yes, I added a video. As you can see in the video (hopefully) I flew about 100 blocks, but the statistic says I flew about 200 meters. I'm fairly confident 1 block is one meter in Minecraft, but I could be wrong.

1 block is indeed 1 cubic meter, do note that you aren't flying in a perfectly straight line, so it should be a little over 100, double is still wrong though.

Can confirm this. I dropped from y=120 to y=90 with the elytra enabled twice. On the first time, the statistic increased 59.72 m instead of 30m. On the second time, it increased 59.78 m. I made sure to fall nearly straight down, so the movement on the x and z axes was negligible and should not make such a difference on the statistic.

Can confirm on versions as early as 1.10. In 1.9.x the statistic is also slightly higher than the real value, but only with a factor of around 1.3~1.5.