Windows RT is dead and it was basically a Widows Phone like mobile OS, only for tablets.They did. It's called Windows RT, and later Windows 10 S. You have to use Edge as well.
If the device was ARM, the bootloader was locked into Windows.
It was in direct response to Chromebooks and Android tablets, and adopted the same business model as Google: free OS supported by the content they sold. Because it came on extremely low-end devices, people understood this.
Windows 10S can be upgraded to regular Windows that allows to run/install exe. applications.
Anyway he was most likely talking about the regular Windows 10 Home or Pro that runs on X86 computers.