What details about the Harvest Feast suggest that Ishi and his family are the last of their tribe?

The Harvest Feast is obviously an important celebration because the family indulges in an abundant meal, they sing and dance and the women wear special clothing. However, in spite of the fact that this is an important occasion, the seven members of the family celebrate alone. No other Indian families join them in this feast, which suggests that there are no other Yahi around.