First, let's establish the proper definitions of each term:
The clearnet: the publicly available internet. This is the surface web, the part of the web that can be accessed by search engines.
Darknet: A darknet is an overlay network within the Internet that can only be accessed with specific software, configurations, or authorization, usually using a unique communication protocol.
Hidden services: Hidden services or onion services are the websites that make up the dark web. These websites are still part of the internet, but do not want to be found. They make up a sliver of the deep web (the deep web is the internet that cannot be indexed by search engines). Hidden services end in a ".onion" and their url is usually made up of a sequence of random characters (for example DuckDuckGo's hidden service, has a URL of 3g2upl4pq6kufc4m.onion). These hidden services can only be accessed with the Tor network (a darknet) which is configured to access hidden services.
Now that we know what each term means, let's answer the question. Now the tag's definition is a little confusing, but basically the tag is sort of right. It says:
"Clearnet applies to any outside service on the regular Internet"
which is true, given that the "regular internet" means the surface web which is what the clearnet is. However, what is a little confusing is that the tag also states that hidden services may access the clearnet. But what this means is that hidden services may also use features or things that are from the normal internet such as Captchas, etc. And if you keep reading the tag, they provide and example where the Silk Road used a Captcha (which is from the normal surface web) which is how they got caught. What the tag says is true, albeit in a confusing manner. Just stick with the definition above.