Hinata is not Hamura's incarnation, nor was any indication given to believe so.
Hinata met Hamura due to outside forces, rather than him appearing from within her. Hamura's appearance was also preceded by a flashback to the war between the main/branch houses of the Otsutsuki, in addition to the entire main branch appearing before Hamura arrived. Anyone with the byakugan that was in the room at the time would have seen the images, as it only reacted to the byakugan.
Lastly, the situations are different. Hagoromo appeared inside of Naruto and Sasuke, but neither of them were his incarnation. Though they were his sons' incarnations neither of his sons appeared in their mind. In the same way, Hamura appearing to Hinata (mind you, after many other people appeared to her) would not mean anything. He appeared to give her the chakra because it was the only way to stop Toneri's plot, and only she would be able to receive it.
What do you think?
