It says outside the shower. In Bosnia, the shower was the only place we could go without our weapon. Just going for a crap- you had to take it, but for the shower it was allowed to leave it with a buddy back in the tent. The rationale being, you wouldn't want to take your weapon into the shower with you and while you were in the shower you wouldn't really be able to watch it while it was propped in the corner of the shower room. It's only a few minutes of a soldier's day and if you're within an armed and guarded camp, it's not like it's a huge security let down.
Furthermore, I don't know what the weapons status is for off duty personnel on this particular camp but it could very well be that off-duty soldiers are not walking around with magazines inserted in their weapons. In such a situation, they would have the magazines with them but not physically in the weapon. Therefore, it wouldn't be all that hard for an attacker to overwhelm someone before they could get a magazine into the weapon.