I don't know. I guess he decided that just having the bike in the cage was secure enough. If that's the case, I can understand not wanting the hassle of going to the security guard to get his bike unlocked. It's probably the exact hassle he was hoping to avoid by not locking his bike up in the first place.

That said, I've forgotten my lock once or twice and had to place my bike in a somewhat secure place, but not as secure as actually locking it up. If someone had gone the extra mile and locked it up for me, I would have been grateful.

Also, I can certainly see why security would want bikes locked, even if they were in the cage. The cage is really just one more barrier against theft. A bike thief looking for the easiest score might see unlocked bikes in the cage as a way to get multiple bikes by only breaking one lock. However, if requiring bike locks on bikes in the cage is going to be a policy, they should make people aware of it.

So, yeah, I can see where, if you made a conscious decision favouring convenience over safety, you might be annoyed to find that someone had reversed your decision. But it's probably not the decision I would make.