Legitimate versions of GTA V are over 100 GB. Downloads claiming to be as small as 18 MB or "highly compressed" are technically impossible for a game of this scale.
The search result highlighted a single name: Henderson, Mr. Legitimate versions of GTA V are over 100 GB
If your GTA 5 download was under 30GB, it is unlikely to be a functional version of the full game, as the core assets (audio and textures) cannot be compressed that significantly without losing all quality. Legitimate versions of GTA V are over 100 GB