My friend shared on Facebook the page https://ja.wikipedia.org/wiki/ミルグラム実験
Here is the article preview shown by Facebook, the article is not about broomsticks, the thumbnail presumably comes from the cleanup template:
The article contains this image, which would have been a much better thumbnail for the preview:
https://commons.wikimedia.org/wiki/File:Milgram_Experiment_v2.png
I am not sure whether the problem is Mediawiki or the configuration of the Japanese instance, or something else. Possibly related: T142243