This is somewhat misleading. You are correct that there was a treaty. However, the express wishes of the people of Hawai'i were independence and this treaty was REJECTED by the US Congress after petitions from Hawai'i. Following this a piece of legislation called the Newland resolution. This is not news, and in fact googling "Treaty of annexation [...]" as you suggest the only link with your treaty in the title is an anglefire website which is hardly credible. 

Every other site links to the Newland resolution as this was in fact the device by which Hawai'i was annexed. 

Similarly the legitimacy of this act is highly questionable. As indicated by the petitions, the population at large were opposed to annexation. It is a bit like president Maduro's recent election of a constitutional assembly--wildly opposed by the population and pushed through with a veneer of legitimacy to shore up the interests of someone whose hold on power is in danger and highly questionable.