Ghost station or outpost with frontier

[Grizzligris]

There might have been a civ or a station that settled there , but eventually all I saw was this ghost element on top of Giant Fungus with a frontier. Is this a bug?

 

[Ryika]

Uhm... "ghost element"?

The green borders just show that the tiles around the fungus get +2 extra food (shows up after it has been activated).

 

[Grizzligris]

By "ghost element" I meant missing outpost or city with Giant Fungus on top and a frontier around.
Turns out, it is a normal and actually a cool game feature.

This video at 21:20 actually answers my question as well.
https://www.youtube.com/watch?v=NDRpsCVRQ8Y&list=PL-lTq9LJCHpRhp7tP5ynqwOEeMlcNpQ1b&index=13

Thank you.