This isn’t really correct.
For the topic case https://cards-dev.twitter.com/validator shows
For the post case https://cards-dev.twitter.com/validator shows
I tend to agree that we should normalize behavior here, in the first case.. when no image exists in the first post, go ahead and use the site logo cc @techAPJ
But note that the link on your twitter refers to a post that does not exist:
https://forum.intercoin.org/t/wall-st-conference-at-mar-a-lago/391/2
There is no post #2 in that topic..