This is a good example of a design team that has too many things going on.
In a past design of the Twitter web app, the “collapse entry” icon was located in the header bar (I think it even said “Collapse”). It has since been moved down into the feed attached to specific stream entry. Where previously it was a common, centrally located icon used to collapse all open entries, there is now an explosion of similar and confusing icons + mismatched labels. The icon (historically an “open new window” icon) is doing the work of multiple actions.
It says to me that no one is minding the gap … by which I mean there is some communication or process issue that leads to this kind of design. It’s also an example of how hard icon design can be… from memory, I recall that the past collapse icon may have been a hamburger menu… which may not been the best choice either.
I’d love to see the data that lead to removing the collapse control from the header, but I think the explosion of iconography indicates some other issue. I have a hard time believing that users grasp the distinction between all of the above icon/label combinations.