This is a glitch appears in previous version till present. (version 1.11.3)
This happens when you are chased with a random zombie, you enter in a room and stand next to a thin wall while you are also next to the entrance.
This glitch appears often in Motel and Bunker Alfa. The reason of this trick appears might because enemies attack player automatically (for sure it's automatically) in their attacking range, and if you stand next to the wall and the entrance, the enemies will start attacking you from the another side of the wall, since the game system determines this as "the zombie is hitting the wall, not the player." You won't receive any damage, but you couldn't cause any damage either.
From those description above, you might think this wall trick is an useless bug, but you can use it to immune damage from the enemies especially Frenzied Giant, and you can walk out and deal damage after the enemies attacked and go back before the enemies try to attack you again.
Theoretically, you can use this trick to kill a Frenzied Giant with crowbars, but if you make a mistake, you might receive damage from the enemies. And the amount of the enemies you need to deal with, the attacking speed and the enemy attacking speed will affect the chance you immune damage.(or receive)