That article was quite misleading and inaccurate. Disregard everything you read in it.
If Caddy is preforming HTTP-01 validation, the following page rule that I have used with Let's Encrypt and Cloudflare may interest you, as it keeps the challenges on port 80.
There are better ways to manage those settings than via a Page Rule, but I haven't posted my updated configuration here or in the Cloudflare Community yet.