GO - Package name of files

I learnt that, all .go files in a directory must name the same package.

Considering below example from github,

fogleman/nes/
  nes/	
    apu.go	
    cartridge.go
    console.go	
    controller.go
    cpu.go	
    filter.go	
    ines.go	
    mapper.go	
    mapper1.go	
    mapper2.go	
    mapper3.go	
    mapper4.go	
    mapper7.go	
    memory.go	
    palette.go	
    ppu.go	
  ui/	
  util/
  .gitignore	
  LICENSE.md	
  README.md	
  main.go	

So, All .go files in directory(../fogleman/nes/nes) have the package name nes(same as directory name).

Similarly, all .go files in directory, ../fogleman/nes/ui have the package name ui(same as directory name).

Considering below two files, I have a question,

1)

roms.go file in directory(../fogleman/nes/util) has package name main(different from directory name)

2)

main.go file in directory(../fogleman/nes) has package main(different from directory name).

Question:

Why package name(main) is different from its directory name?

I believe the author of this repo intended on running roms.go as a separate program for testing. Without putting this file in package main, this could not be done. If you are in the root project directory:

cd util

go run roms.go path/to/roms/dir