If you want to reproduce this, one way is to come up to water pump with nothing in your hands. Then you spamm press "F" and then take Axe for example to you hands...

I tried this. But I did something else as well and this bug showed agian. I was playing normally I didn't spamm anything and this is what happened.
I think I was lying down, l was holding an axe in my hands, then went in inventory and I ate some food, when he took his Axe in hands again, it was crazy.

If you want to fix this, you need to relog, because you can not throw or remove the axe (gun) from your hands... you can walk normaly, open doors, crouch, prone, AND when you switch to First Person The arm is in front of your eyes, half of the screen is covered by arm...

And you can not attack with axe ! it doesn't let you anything with the hands.

Thanks.