The current theory is based on comparative linguistics, which show that Hawaiian language is closely related to Marquesan (another Polynesian group), but with later borrowing of terms from Tahitian.  Hawaiian tradition associates the Tahitian influence with Pa`ao.  This is probably the theory you heard.

I'm not sure where @diverdave got the idea that Polynesians weren't the first Peoples of Hawai`i.  @diverdave has been reading a lot and I'm curious where this idea came from.