I'm going to go with that old chestnut: It Depends. The author gives a variety of scenarios where the session could be stolen, but doesn't really discuss the context and threat models around them. There is no one-size-fits-all. Shorter expiration times might be the right choice in some scenarios, and useless in others.

Also, yes, shared computers without user separation are still a thing. Not all libraries have the budget or technical expertise to secure shared computers as well as possible. Also, there's public WiFi, something I'm betting the author uses all the time.