I don't know where you got that, but you better hope they run after you pull your weapon if you think that. Because if you leave 4 unarmed people dead in an alley without evidence of battery on you, you're gonna probably get the needle unless they left behind a note or something saying they were heading out to mug people.
If you fear for your life and are not a willing participant and don’t see a way out without using force, you can do that.
Read up on disparity of force.
It’s not something I’d ever encourage someone to want to do, or be excited about doing. But when multiple assailants are facing you and you believe you are in imminent danger and fear dying or permanent bodily injury, you are able to defend yourself. If it’s 4 against one you are at a disadvantage and 4 of them can permanently injure or kill you, so use of the firearm against them is reasonable under disparity of force standards. It is even more warranted if you are old and they are young, if you are disabled, if you are smaller, if you are female and they are male.