User blog comment:The ASL Pirates/Haoshoku Haki Theory/@comment-71.13.82.131-20150216150346

Not sure who said it, be it in the chapters or the SBS, but Kenbunshoku and Busoshoku are said to be in all people. So for Ussop to have tapped into this it is no surprise, same as Coby gaining it during Marineford.