Verse 4.4.5

तं होवाच नैतदब्राह्मणो विवक्तुमर्हति समिधं सोम्याहरोप त्वा नेष्ये न सत्यादगा इति तमुपनीय कृशानामबलानां चतुःशता गा निराकृत्योवाचेमाः सोम्यानुसंव्रजेति ता अभिप्रस्थापयन्नुवाच नासहस्रेणावर्तेयेति स ह वर्षगणं प्रोवास ता यदा सहस्रं सम्पेदुः ॥ ४.४.५ ॥
॥ इति चतुर्थः खण्डः ॥

taṃ hovāca naitadabrāhmaṇo vivaktumarhati samidhaṃ somyāharopa tvā neṣye na satyādagā iti tamupanīya kṛśānāmabalānāṃ catuḥśatā gā nirākṛtyovācemāḥ somyānusaṃvrajeti tā abhiprasthāpayannuvāca nāsahasreṇāvarteyeti sa ha varṣagaṇaṃ provāsa tā yadā sahasraṃ sampeduḥ || 4.4.5 ||
|| iti caturthaḥ khaṇḍaḥ ||

5. Gautama said to him: ‘No non-brāhmin could speak like this. [Therefore, you must be a brāhmin.] O Somya, go and get me some fuel [for the sacrificial fire]. I will initiate you [as a brāhmin by presenting you with the sacred thread], as you have not deviated from truth.’ After the initiation, he selected four hundred feeble and famished cows. Addressing Satyakāma, Gautama said, ‘O Somya, take these cows away [and look after them].’ As. Satyakāma was taking them away, he said, ‘I will not come back until there are a thousand of them.’ He lived away for many years until they had become a thousand.

Word-for-word explanation:

Tam ha uvāca, he [Gautama] said to him; na etat abrāhmaṇaḥ vivaktum arhati, no non-brāhmin could speak like this; samidham āhara, get some fuel; somya, O Somya; tvā upaneṣye, I shall initiate you; na satyāt agāḥ iti, you have not deviated from truth; tam upanīya, having initiated him; kṛśānām abalānām catuḥśatāḥ gāḥ, four hundred thin and famished cows; nirākṛtya uvāca, having chosen, he said; somya, O Somya; anusaṃvraja iti, take these away; tāḥ abhiprasthāpayan, as he was leaving with them; uvāca, he [Satyakāma] said; na āvarteya asahasreṇa, I will not come back until they are a thousand in number; saḥ ha varṣagaṇam provāsa, he lived away for a long time; tāḥ yadā sahasram sampeduḥ, until they were a thousand. Iti caturthaḥ khaṇḍaḥ, here ends the fourth section.

Commentary:

The point is, no matter what Satyakāma’s birth was, he had the qualities of a brāhmin—love of truth and learning. Though he had to suffer much hardship living in the forest looking after the cows, he was more concerned with keeping his word than with seeking physical comforts.