How is it irrelevant?

FTP is a protocol, but people use FTP in a variety of wrong but commonly understood meanings:

FTP Server = Hard drive accessible via FTP, not the server on that machine running the protocol

FTP Program = a file-management interface that uses FTP protocol to send commands

HTTP is also a protocol, though 'web browsers' can browse other protocols, as well as offline files.

Saying that an FTP Client that contains support for S3 is a misnomer is like arguing that accessing a file from your desktop using a 'web browser' isnt correct since you arent browsing any web.

The list is aimed at demystifying the confusing terms for the layman, its not aimed at providing the most technically correct taxonomy (since that would also not communicate much to the layman)

When I use my FTP client for SFTP am I using FTP or SSH?

What layman who can't understand ftp is a protocol and doesn't mean any kind of storage, needs to understand the meanings of aws services?

If you're using sftp you're using ssh. It doesn't matter if your client also talks to ftp servers.