Indeed the size calculation is incorrect. It's likely looking at the unpacked size, but snaps are never unpacked, which ironically is a difference missed by itself.

These are the actual sizes for these 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 -