Thanks for playing.
The initial idea was that you could pick guns back up and that you would get new guns from chests. I eventually scrapped that as I felt it didn't feel so nice with the limited ammo mechanic; so yes you're not supposed to pick up old guns. The chests had potions in them that heal you, if you're standing below the chest you instantly pick it up, this is a bit of a visual/feedback issue I agree.