You're misreading that comment. It does not say what you think it says. What it says is "I wrote MicropolisJS. Someone else took that code and stripped out the licencing headers, and that version is used in 3D.City".

Mocropolis is released under GPL. MicropolisJS is released under GPL. Someone took some code from MicropolisJS and removed the header, and that code is used in 3D.City. The person who removed the licencing headers is not the author of micropolisJS.