The Sign of the Beaver is told from the point of view of a narrator who speaks through the voice of just one character. This means that the novel is told from the third person limited point of view. The narrator, and so the point of view, for the novel is Matt.
We know this because throughout the novel we are exposed to Matt's thoughts and feelings as if we are inside Matt's head. However, because the author did not use the pronoun "I" throughout the book, and instead used the pronoun "he" or simply referred to Matt by his name, we know that the book is not written in first person. A third person limited point of view such as that used in The Sign of the Beaver means that the narrator knows and expresses all the thoughts and feelings of just one character. In this case, that character is Matt. It is through Matt's voice and point of view that we learn about the thoughts and feelings of the other characters.