@canemorto Those survivors were not "friendly" ones, they are classed as neutral.
Sorry for the large amount of text but I kinda get in a zone when I start writing and I don't get out of it until it's too late.
Friendly - Appears out of nowhere usually and says something along the lines "Lets team up!". He will then follow you and assist you in fighting hostiles (like a pet in other games). I have not been in contact with one for long enough (they kept shooting me by accident) but it appears that you can't give them equipment/trade with them.
Neutral - These are usually found on a stretch of road, most of the time in groups. These "groups" will stay where they are, so once you have found them your set. They don't shoot at you specifically but will start shooting if you attack first. Also bear in mind that they don't know what collateral damage is, so make sure there isn't a zombie or wild dog somewhere behind you in relation to them, as they will fire at the thing, with you in the middle. When you are close to them a button will appear with a speach bubble, this allows you to trade with them for different things. Another good thing to do is to set up base near them, as they will act as permanent sentries.
Bandits/Hostile - Most common, they roam the map looking for the player. If found they attack on sight, usually have a melee weapon but in later stages of the game they do get guns/rifles (they are terrible at aiming however). Only word spoken by this class is taunts or pleas for forgiveness (depending on how the fight is going).
*Note* All survivors can and will eventually die. When they do they drop all their equipment. Also I have yet to double check this but it appears that survivors will search building and collect loot, as I have found in numerous instances that I have left a tool/weapon and when I returned it was missing. 15 or so game minutes later I find a bandit with that exact tool.