Just to be clear, Visual Studio does not officially run on anything other than Windows.
However, as the linked blog post indicates, since this is .NET based you can use any IDE or code editor you like that has support, such as Visual Studio Code, or JetBrains Rider, which are available for Linux and macOS.
The game engine’s own editor is also Windows only and presumably if that is .NET based then one day it might be cross platform if the community makes it happen. That doesn’t really relate to Visual Studio though.
My guess is a typo, possibly supposed to be 11 or 12? Is 1998 too early for TF2 design to be occurring?
According to Wikipedia. So that looks plausible.
The post however talks about gathering feedback from players of TFC, which didn’t come out until 99. Maybe Robin meant the original mod, which he also worked on, or maybe he just misremembered at what point TFC came out or when they actually explored the death stuff that resulted in the freezecam.