It's the same in Chinese and Japanese. It helps a lot that the letters are designed fit into individual square blocks. The blocks can be arranged any way you want. There have been internet memes, for example, written to mean one thing when you read left to right and a completely different thing top to bottom.
But yes, Chinese was written top down, right to left. The PRC basically switched over to left-right, top-bottom right away (it kind of went hand in hand with the simplification project). Taiwan for example kept the traditional format for a lot longer.
When I was learning Mandarin in the late 90s, all our imported material from Taiwan was still top-down, right to left.
Here's an example Taiwanese newpaper from 1993 (yes, that's Michael Jackson) https://www.taipeitimes.com/images/2021/08/29/p08-210829-fro...
You can see the body text is arranged top-bottom, right to left, and the headlines employ a mixture of approaches.
There's not really a distinction. Chinese was written in columns from right to left. When the columns were one character long, they were still columns.
To distinguish horizontal writing from vertical writing, you'd need a writing sample that had multiple columns and also multiple rows. (Because, as noted above, there's no way to tell the difference between 1 row of 5 characters vs 5 columns of 1 character each.) As far as I'm aware, traditional Chinese writing is fully accounted for by the theory that it was always written in columns and never in rows.
On the other hand, the Taiwanese newspaper isn't making a great case: the "mixture of approaches" used in the headlines are a couple vertical headlines going top down, and several horizontal headings, including the primary headline "Michael Jackson、arrives!", which all go left-to-right. The body text in the infoboxes in the top left and right corners of the page also goes from left to right, though it appears to be true that the article text is in columns. The name of the newspaper (top center) is also printed left-to-right.