In the old blogging software I created back in the 1990s, I had a handful of posts types
There was a type of rich-text oriented post that had a title. (Article)
And, there way another type of rich-text oriented post that did not have a title. (Note)
(There were also other types of posts, but they aren't relevant here)
These 2 types of posts were rendered / displayed differently
I.e., my 1990s software already had this distinction
@reiver@reiver ⊼ (Charles) 
there's a page on this in the primer:
https://www.w3.org/wiki/Activity_Streams/Primer/Article_and_Note
But it's not always clear.
One thing that might distinguish is presentation.
I expect an Article to appear on its own page. References to an Article in a stream or tree layout might just include title and summary, with a link to a UI to show the full text.
But lots of Note objects can fit in a stream or tree presentation.
If you have a fediverse account, you can quote this note from your own instance. Search https://cosocial.ca/users/evan/statuses/116110492780799145 on your instance and quote it. (Note that quoting is not supported in Mastodon.)
