One rule I have always lived by is "trust no wild animal under any circumstances." Wild animals process fear completely different than humans. Once I came upon a deer hunter that had been gored by a buck deer. He told me the animal was down then got up and charged him. Cougars are the same rule. They might run and as a rule do, but they can turn and attack. Bigfoot is thought to be a primate as far as I know. Primates are known to be temperamental as we have heard of monkeys turning and injuring their keepers.
Bigfoot is powerful enough to kill a human with full intentions of just running him out of the territory. There is too much evidence now that bigfoot can be extremely dangerous to humans. Their fascination with small children make them even more dangerous because you have human adults nearby willing to fight for their kids survival, and a bigfoot that might take any action as an attack on itself.