Clarification: not just these 2 countries. I wonder if all countries do it.
Some countries go above and beyond; Russia typically grants overflight access to one airline per country, so SAS has the ability to fly over Russia while Norwegian Air never has.
In any case grandparent poster is probably just repeating info out of this video: https://www.youtube.com/watch?v=jdNDYBt9e_U&t=382s