It’s not. It just has really heavly modified Linux kernel and the similarities end there. Termux uses a hack that was already patched, so if Termux ever update to newer API level it won’t work.
I hate how files, the UI and overall services managment work on Android. I cannot mount a drive, access app’s files and their configs, I cannot change the UI environment or system theme (besides basic setting of app launcher and dark/light), I cannot update beyond manufacturer support and swap OSes like on PC and the list goes on…