Piping is implemented in the shell (bash, zsh, etc...), not the unix commands themselves nor the terminal emulator. Whether the above discussion was using the word "terminal" to refer to the terminal emulator, the shell, or the whole combined experience is anyone's guess.

Piping is a feature of the shell, not the terminal.

But composable means that cli tools produces text, consume text, and are configured through text. You can build independent tools to do separate task and then build a meta tools that coordinate them. While the individual tools may be complex, the coordination can be very easy. With posix shells, you have piping and subshells that do a lot of the heavy lifting.