A PC wields a 1-handed weapon one-handed. He wants to make a disarm attempt with his empty hand. The PC possesses the feat Improved Disarm but not the feat Improved Unarmed Strike or any other similar ability.

I think that the PC provokes an attack of opportunity for making the disarm attempt unarmed. Put simply, I read disarm as an attack.

The PC's player claims that his PC does not provoke an attack of opportunity for three reasons:

1. A disarm is not an attack as such, but an attack-equivalent action, which he simply interprets as a standard action.
2. The Improved Disarm feat overrules the unarmed strike rules in this particular case.
3. The PC's considered armed because the PC's still wielding a melee weapon.

Who's right?