It's not true.
Also, Cydia doesn't create an sftp server when started. It's a client for an APT repository. I'm not totally sure on the workings of APT, but it's a client because it downloads files from a server.
You may be thinking of OpenSSH. That doesn't drain battery either because it's only active when data hits port 22 on the phone to start the phones SSH or SFTP server 😀