Huh ?? It's not like GTA3 invented anything at all !
Look at RPGs like Ultima7 in early 90s, it simulated a whole living world, way more complex that GTA, and you had total freedom to explore it.
Same for the Elder Scrolls series, many years before GTA.
This guy is just behing very ignorant to credit GTA for this. Sandbox games have existed for DECADES.