Theory on where the leaks are sources from
The leaker most likely has a build restricted to just the beginning of the game before you even encounter Lucia. The cutscene with Cal appears to be early game (just a guess), theres zero lucia content, the only missions icon is ‘C’ (probably for cal) theres constant tutorial popups throughout the footage, jason wears the same clothes meaning its all the same build, he’s at his starter house, he has hardly any money, has the starter car, and has very beginner weapons.
Like the comment said, sometimes gaming companies give very restricted builds for QA. This is almost certainly what happened. Which is why there hasn’t been any story leaks or lucia gameplay.
This also makes it even easier for rockstar to ID the leaker. They know exactly what build this by the context and the placeholders.