Late to this, but here's my two cents.
8-9 million years ago, dryopithecines in Africa split into two lines - one that led to gorillas and the other to humans, chimpanzees, and bonobos. At 7 million years ago, another split happened between chimpanzees and bonobos from early ancestral hominins that became humans. I've heard during the Miocene epoch, there were at least 50 types of great apes. I think bigfoot originated somewhere back around there, probably interbred with early humans (it seems we slept around a lot, since we also have Neanderthal and Denisovan DNA), and became a new species. It self-selected to become nocturnal and gigantic size, which is our opposite. They and us are similar, but we share this world by occupying opposite niches - we are tool users, hairless and live our lives in communities, being out and about primarily in the daytime. They don't need tools, rely upon their strength and speed, are hirsute and are primarily nocturnal, living singly or in small family groupings. They are also very intelligent, but in different ways. So, yes, in the great ape family, but similar to how we are great apes, but more.