Why is a soft link to fcgi-bin/lsphp5 required when installing OSL?

In the official installation guide you are told to create a soft link as follows:
ln -sf /usr/local/lsws/lsphp73/bin/lsphp /usr/local/lsws/fcgi-bin/lsphp5

1. Is this optional (i.e. only if you plan to use fcgi), or required? I see no overview presented of OSL's architecture. I have only ever used php via mod_php in apache, and never given any thought to cgi stuff before. Is fcgi the only/primary php interpreter in OSL?

2. It feels ugly/hacky to me to link a version-7 interpreter to something labelled fcgi-bin/lsphp5. Why not link directly to fcgi-bin/lsphp?
The doc is here:

By the way -- this documentation could do with an update to include Ubuntu Server 20.04, where things are a bit easier than in previous versions (e.g. certbot repo doesn't need to be added).