From your source: "Microsoft's internal project name for the new OS was OS/2 NT, because Microsoft's intention was for the new OS to succeed OS/2 yet retain the OS/2 API as
its primary interface."
Note how Russinovich talks about a "new OS".
The NT (kernel) never had any OS/2 code in it, it was a totally different project. The first target processor architecture for NT wasn't even x86, it was MIPS.
OS/2 in NT was merely a subsystem layer next to DOS and Posix, somewhat like today there is the Linux subsystem layer in Windows 10.
A good source is this:
I thought it's pretty well established now that the NT in the name was named after the target architecture: Intel i860 "N10", not MIPS.