Snaps size computation in the article is wrong according to official documentation https://docs.snapcraft.io/t/the-snap-directory/2817

Yes, the size is wrong. It's looking at the unpacked size, but the snaps are never unpackaged. Here are the actual sizes for the mentioned snaps:

  $ snap info vlc | grep stable:       
  stable:    3.0.4                   (555) 204MB -

  $ snap info libreoffice | grep stable:      
  stable:    6.1.2.1 (86) 501MB -

  $ snap info gimp | grep stable:
  stable:    2.10.6 (47) 192MB -