alt Hacker NewsI'm always surprised that papers don't include some "chat" apps as social media. I don't see Discord mentioned in this paper but I use it almost identically to how I used Facebook in like 2010 and at least among people I know that's very common. I think the use cases from more traditional "social media" has migrated a lot back to chat apps and those still provide a lot of value and are more widely used than ever.
Terminology shifted somewhere along the lines, because the nature of sites like Facebook changed. These sites were called "social networking" in the early days, since they connected people. These sites are called "social media" these days, which I assume is a reflection that the top-down nature of these sites are much more like traditional print/radio/television media.
The treatment of chat applications, online forums, etc. as social media has always felt strange to me for that reason. While the companies that offer those services may control the platform, control of interactions is limited to moderation and the content of those interactions is rarely created by a commercial interest.