The blog says the destination was Oakland. The Oakland International Airport is at 37°43′17″N 122°13′15″W. The data packet also contains the current lat and long of the flight as 40.201 and -100.755 respectively. Plugging that in to a distance calculator [2] gives 1163 miles, 1010.6 nautical miles, or 1871.6km. So the distance value of 1167 appears to be miles.
At 487mph covering 1163 miles would take 2.3963039014 hours or ~2h23m. If the speed is knots then it would be 2.08233112598 hours or ~2h5m at 560.4296mph. So mph makes the most sense given an estimated time of arrival of 2h25m.
So I think you are right, the distance appears to be miles and the speed MPH. This makes sense for an in-flight infotainment system on a US domestic flight.
The difference between 1167 and 1163 can probably be explained by the fact that the plane is 6.5 miles in the air traveling at 8 miles per minute and we don't know update interval or if the distance is in the air or on the ground.
[1]: https://geohack.toolforge.org/geohack.php?pagename=Oakland_I...
[2]: https://www.omnicalculator.com/other/latitude-longitude-dist...