Broken html

Could be a one-off case.

The html source has broken tag or maybe unclosed tag, so sidebar is leaking into body, normally they have this DOM:

- .primary-content

+ article.post

- . sidebar

This page has:

- .primary-content

- article.post

- .sidebar

As you can see there's no such issue in other pages, catching all those one-off cases make a little sense.

Also, in the source page they have:

That Copyright 2018 ... text is wrapped in blockquote.twitter-tweet, you generate embedded twitter, you lose that copyright texts.