A file is smaller than a single GTA V mission file. To claim 100MB is to claim a compression ratio of 1000:1 —something that does not exist for modern, complex game data.
Pros:
For a deep dive into how the game performs on various hardware setups and how to optimize it: 48s gta v highly compressed 100mb
True data compression has limits. While professional "repacks" from known groups can reduce the game's initial download size to around 35GB to 50GB A file is smaller than a single GTA V mission file