Sankara makes no reference to the Rig Veda in his comments to these verses, however, Both Swami Nikhilananda's and Swami Madhavananda's separate translations footnotes the three Rig Veda verses you mentioned, but no footnote on verse 18.

Both Swamis Madhavananda and Nikhilananda in their separate translations reference that verses 16 and 17 refer to the Pravargya rite from the Satapatha Brahmnana (XIV. i. 1. 6-10.) and also the Taittiriya Aranyaka (V. i. 3-6.)

They both have a slightly different translation to verse 18 which I think are clearer translations. Nikhilananda's and Madhavananda's translations are essentially the same. Madhavananda's translation says:

..."He (the Lord) made bodies with two feet; he made bodies with four feet. Having first become a bird (the subtle body), He, the Supreme Person, entered all bodies. On account of His dwelling in all bodies (pur), He is called the Person (Purusha). There is nothing not covered by Him, nothing that is not pervaded by Him."

Sankara makes no reference to the Rig Veda in his comments to these verses, however, both Swami Nikhilananda's and Swami Madhavananda's separate translations footnotes the three Rig Veda verses you mentioned, but no footnote on verse 18.

Both Swamis Madhavananda and Nikhilananda in their separate translations reference that verses 16 and 17 refer to the Pravargya rite from the Satapatha Brahmnana (XIV. i. 1. 6-10.) and also the Taittiriya Aranyaka (V. i. 3-6.)

They both have a slightly different translation to verse 18 which I think are clearer translations. Nikhilananda's and Madhavananda's translations are essentially the same. Madhavananda's translation says:

..."He (the Lord) made bodies with two feet; he made bodies with four feet. Having first become a bird (the subtle body), He, the Supreme Person, entered all bodies. On account of His dwelling in all bodies (pur), He is called the Person (Purusha). There is nothing not covered by Him, nothing that is not pervaded by Him."