When we talk about a version of a game, we aren't talking about a simple ZIP file. Standard compression (like WinRAR or 7-Zip) usually reduces a 5GB game to around 4GB. Highly compressed versions use advanced algorithms (such as LZMA2, Brute Force, or Repack techniques) to shrink the game down to 1.5GB or less.
Crucially for low-end users, v1.30 was less demanding than v1.40+ (which added major graphical overhauls like DX11 lighting). It runs smoothly on 2GB RAM and integrated graphics. Euro Truck Simulator 2 Version 1.30 Highly Compressed