I assume the author meant to emphasize reading. And when you try to speed-read/browse multi-column layouts, it's becomes slower because your eye needs to cover a larger horizontal area.

For example, when Flickr transitioned from a single-column to the current row-by-row clusterfuck, it became much harder to quickly find a particular image in someone's photostream.

Also, example.tumblr.com/archive, which has the added advantage of not using people's themes.

I would only consume the archive of tumblr blog that is primarily photos that way. Trying to read a mostly print blog that way would be difficult.

Tumblr is a black hole of awful UI design. You can't even use god damn tabs with the default theme.

I certainly have a hard time seeing either Trello or Jira without multiple columns.

There isn't anything enjoyable about a wall of posts honestly. I'm glad that trend on every copycat site died out.

Also literally any table, but that's not what the author meant.