Is Unetbootin capable of making any iso file bootable

1)It is a great experience to achieve what I got today. I had downloaded GParted iso file (135 MB size). Now to make a bootable usb of it, I used unetbootin and to surprise I succeded in entering Gparted application and modified my partitions.
Earlier I was in a notion that it is used only for installing Linux by making bootable usb,etc. so, can it be used for any iso?

2)As I had earlier installed OS, I had to specify where I want to install it. But in this case (point 1) where I made bootable usb of Gparted iso: when I booted my system by doing the appropriate BIOS set up, It didn't ask me where to install Gparted. Directly I entered the Gparted application. So, please clarify me what happened in this case. Did it install in USB drive only?

3) When I entered the gparted application, there I opened a terminal. When I entered command

shutdown -h now

it asked me for root password. Because while booting from usb, it nowhere asked me for root credentials. so what is root password.