To be precise, it allows "Unarmored (dog)" armor.
So, you rush up the stairs and...kill infector the same way you kill zombie. Or would you allow it to roam free in the hospital first? For "extra fun" and all that.
Correct, but if you try to bring an unarmored dog to the actual mission, it will not allow it. I think it's just a documentation error.
Yes, the intent of the infector is to make the mission a bit more challenging and/or unpredicable, as well as giving players another way to obtain an Infector (which can be problematic due to RNG).
The current zombie is always just a plain zombie. At most, it can kill a few of the civilians before it dies itself.
Plus, the description implies that there's an outbreak / patient 0. Right now, there is no chance of that since it's impossible for anyone else to be infected.
The spread could become kind of bad, but it won't be too bad since the created zombies are just regular zombies rather than infectors. I'm not sure if X-Com Files has the same quirk that the original X-Com and TFTD did -- where the Infector will keep attacking the same target. That would further limit the spread by effectively ensuring that only 1 zombie can be created per turn.