My guess is that apps written in java/kotlin are easy to run in a x86 compatible android runtime.
The difficulty is for native code, the arm libraries embedded in many apps. Actually most Android app depends on native libs. For image processing for example. Nearly all games are using native arm binaries.
The sentence you quoted is probably related to native code only, which is the difficult part. It looks like they have some magic tricks to make them work on x86 architecture with having to recompile the libs.
Intel used the same tricks in their x86 android devices a few years ago, you could run arm native code on their x86 android versions transparently.