If you read the article more closely than I did originally there is an example of what I see in their original article [0]. The thumbnail is part of the list view and they want to see a thumbnail without the other file details.
Yes, they are so small that they are completely useless. What is needed is a widget like the one from Windows at the top of the article that actually shows all the thumbnails at a decent size so you can use them to actually locate the right image.
The screenshot from the article is very low resolution, so it's quite hard to see if you don't know what you're looking for, but it does have a unique thumbnail against each filename.
The underlying complaint is that people want this to be bigger.
[0] https://jayfax.neocities.org/mediocrity/gnome2.png