King Satyavrata, endowed with knowledge and realization by the mercy of the Lord during Cākṣuṣa Manvantara, became Vaivasvata Manu in the present Manvantara. The word tu indicates a different subject, an event occurring during Cākṣuṣa Manvantara. This corresponds to the previous description: rūpaṁ sa jagṛhe mātsyaṁ cākṣuṣodadhi-samplave | nāvy āropya mahī-mayyām apād vaivasvataṁ manum || The Lord accepted the form of Matsya during the flood at the time of Cākṣuṣa Manvantara. He protected Vaivasvata Manu by putting him on a boat made of the earth. SB 1.3.15 The purpose of this avatāra was to give knowledge. This is explained by the phrase “endowed with knowledge and realization by the Lord’s mercy.”