If it helps to understand possible causes of the misreprentation above, here’s a screenshot of an earlier view of the same tweet (probably taken soon after it was posted):
In that early shot, Twitter’s representation was of the first of the three links. There’s the /about text for the forum.
In all later views of the same tweet, in a variety of browsers (including non-extended Firefox 53.0), Twitter’s representation is of the third of the links.
You are referring to oneboxing, which is the opengraph or oembed tags for a page. View source to see what image was selected in those tags, on the target page.
