Neovim is an program that runs in a terminal. You can use it to edit text files and through plugins it can become a fully fledged IDE. The site you linked actually tells you to install Neovim as a package in Termux.
To be clear: Neovim is not a Terminal Emulator. It is not even an Android App. It runs on Android in Termux (and probably other apps), but not on its own.
Termux is afaik the best Terminal Emulator for Android, it includes a package manager with a lot of Linux CLI utilities (like Neovim) available.
idk about op, but if i asked about a good linux tablet, i would mean the hardware not the software
for me a good linux tablet means i can take my favorite linux distro, install it without big hassle and have a good performing computer with all components working afterwards