WordPress is designed to serve a high volume of pages with little to no change to a high volume of users. Write little, read lots which requires little resources to do.
You can use plugins to build gzipped static copies of pages, database queries can be cached in-memory and the whole site can be front-ended with a product such as Varnish.
Most Wordpress sites serve the majority of their sessions to logged-out users.
Discourse on the other hand serves views tailored to the individual. The majority of the users are logged in. Write frequently, read frequently which comparatively requires lots of resources.
There’s really no comparison.
Your test is based on a flawed premise, particularly when you consider this:
Do you load linked resources/assets?
No. Our load generators only know about the URLs you give us when you create a test. We don’t parse the HTML and we don’t download javascript, CSS, or images linked to within pages.
Their test doesn’t even load Discourse correctly.
Source: Loader.io