I had a similar issue where I was battling Zombies at the NE Airstrip. I received a bit of damaged (only bleeding). I killed the Zeds, explored one of the buildings (ground floor), went upstairs, drank a can of drink,, Boom! Broken leg! Thankfully I had sticks in my pack!

Yes your right, The Screen Shot was taken from the SE Mil Camp. I forgot to mention that.

This happened to my mate tonight!!
We were in the building at the NW Military Base. He was upstairs in the room looting it. Grabbed a Green Backpack, then "You are Dead" Appeared on his screen.
His body was outside on the ground, torso on half in the wall!

I agree! Take the SW Airfield for instance...

I have only just come across it for the first time last night (I am still hanging around), with the combination of Zombies seeing you from 100+M away, hearing you,, smelling you,, basically just knowing you're there whether you are sneaking or not.. that along with their super reach for inflicting massive damage when you are 10M+ away from them, and the axe not always registering hits (I'm getting there)
All of the above requires blasting my way out of trouble. That's cool,, when there are too many Zombies, an axe doesn't cut it...
Problem is when I shoot the million Zombies that are attracted to the gunfire only to see more Zombies start spawning from behind me where I just cleared.

So far still have not been able to fully explore the airfield due to unlimited Zombies and are running low on ammo. Its a bit of a bugger.

I have the same problem randomly. Its a bit harder now with the latest update as the Zombies seam to have a reach further than what it looks like they should have, and their hit point look like they have increased.