"This otherwise functions identically to a disarm attempt, as noted above."
ie. just having Improved Unarmed Attack won't negate the AoO
edit: it provokes an AoO because disarm attempts provoke an AoO, and it functions like a disarm attempt, it ALSO provokes an AoO because it's an unarmed attack (if you lack the Improved Unarmed Attack feat)
It still only provokes one AoO even if you lack both the IUA and the Improved Disarm feats, but you have to get both feats (or find other solutions to both sources of the AoO) if you want to avoid it
ie. just having Improved Unarmed Attack won't negate the AoO
edit: it provokes an AoO because disarm attempts provoke an AoO, and it functions like a disarm attempt, it ALSO provokes an AoO because it's an unarmed attack (if you lack the Improved Unarmed Attack feat)
It still only provokes one AoO even if you lack both the IUA and the Improved Disarm feats, but you have to get both feats (or find other solutions to both sources of the AoO) if you want to avoid it