Why extracted .app file appears in Finder 3.1 Mb and in bash only 102 bytes?
.app files are really just folders, but applications (like finder) see them differently and calculate the size of the contents of the folder.

Empty folders have the size of 68 bytes, non-empty folders are 102 bytes or bigger.
All my folders and .apps are 102 bytes since they contain only 1 sub-folder.