This confusion is seemingly caused by the difference in the way passive mode behaves between the original PS3/Xbox 360 release and the so called "enhanced" version released on PC, PS4 and Xbox One.
In both versions, passive mode is only available in "Free Mode". Entering a mission will disable passive mode for the duration of that mission and it will be re-enabled once the mission has completed. Passive mode will prevent you from arming a weapon (except in vehicles, in the original release as discussed below) or otherwise attacking another player or NPC directly. You're still able to drive over NPCs.
In the original version, passive mode is only enabled while on foot - it is automatically disabled while in a vehicle. Additionally, passive players can still be run over or otherwise killed by a player using a vehicle, in that vehicles still hit players in passive mode.
In the enhanced version, passive mode puts the player in a ghost mode, in which they appear translucent to other players and other players cannot physically interact with you while you're in passive mode. When you get into a vehicle that vehicle will also enter the same ghost mode, preventing other players from damaging your vehicle (your vehicle will still take damage from the environment).
Even in the enhanced version, it is still possible for another player to kill you using the environment - for example, blowing up a car that you're standing next to (as the car is "real" for both players) or igniting a gas canister.
Alright, this is just a classic case of a D-Bag modder. If he keeps killing you and you can't do anything, I guess you'll have to unplug your Ethernet or wifi. If you are willing to take the loading screens again force-closing the software will work. On PC you can Alt-F4 and a prompt to close the game will appear, safely closing it.
Best Answer
The short answer: no.
The somewhat longer answer: no, but there are a myriad of ways to acquire money in single player GTA V. One of the more notorious ways is utilizing the assassination missions and the stock market to make massive amounts of profit from the shares' fluctuations. One such guide would be USgamer's article "How to Make Big Money in the GTA V Stock Market". A simple google search for "gta v make money" reveals a myriad of guides for this specific method.
IGN also has a more thorough guide detailing multiple methods of obtaining currency in their guide "How to Make Money in GTA V"