You misunderstood. “Official” can be interpreted in different ways. There’s “official” in the sense that the Caddy team maintains the https://apt.fury.io/caddy/ repo, but it’s “unofficial” in the sense that it doesn’t ship alongside debian.
You probably installed it correctly, but you have two caddy things in your PATH. One from the package we provide, and one from some Python thing. If you do which caddy, you should see /usr/bin/caddy If you see something else, then it’s because something else is taking precedence over caddy the web server. If you run caddy version you should see something like this:
$ caddy version
v2.2.1 h1:Q62GWHMtztnvyRU+KPOpw6fNfeCD3SkwH7SfT1Tgt2c=
It’s up to you to figure out what installed this other “caddy” thing. I’ve never heard of it.
That’s from 2017. Those are installation instructions for Caddy v1. Please refer to our official documentation, i.e. Install — Caddy Documentation.
Like I’ve already said, /usr/local/bin/caddy is not the Caddy Web Server. You installed something entirely different which also uses the name caddy. You need to uninstall that.
By running apt remove caddy, you removed Caddy Web Server, which was correctly installed.
I think I have found the other thing and uninstalled it
python3 -m pip uninstall caddy
That removed
/usr/local/lib/python3.7/dist-packages/caddy/-1.3.2.dist-info/*
/usr/local/lib/python3.7/dist-packages/caddy/*