Bhashya
मनुष्याधिकाराद्वा तद्भावी ब्राह्मणः स्यात् ; 'सर्वं भविष्यन्तो मनुष्या मन्यन्ते' इति हि मनुष्याः प्रकृताः ; तेषां च अभ्युदयनिःश्रेयससाधने विशेषतोऽधिकार इत्युक्तम् , न परस्य ब्रह्मणो नाप्यपरस्य प्रजापतेः ; अतो द्वैतैकत्वापरब्र-ह्मविद्यया कर्मसहितया अपरब्रह्मभावमुपसंपन्नो भोज्याद-पावृत्तः सर्वप्राप्त्योच्छिन्नकामकर्मबन्धनः परब्रह्मभावी ब्रह्म-विद्याहेतोर्ब्रह्मेत्यभिधीयते ; दृष्टश्च लोके भाविनीं वृत्तिमा-श्रित्य शब्दप्रयोगः— यथा 'ओदनं पचति' इति, शास्त्रे च— 'परिव्राजकः सर्वभूताभयदक्षिणाम्' इत्यादि, तथा इह— इति केचित्— ब्रह्म ब्रह्मभावी पुरुषो ब्राह्मणः इति व्याचक्षते ॥
In plain words
Alternatively, because human beings are the ones qualified for this, the person referred to as a Brahmin may be one who is destined to attain that state. The text introduces human beings by stating: 'Human beings thinking they will become all.' It is specifically for humans that scripture declares qualification for both worldly prosperity and liberation—not for the supreme Brahman, nor even for Prajapati. Therefore, through meditation on the lower Brahman combined with ritual, a person attains that state of the lower Brahman. Freed from ordinary appetites, having destroyed the bonds of desire and karma through the attainment of all things, and moving toward supreme Brahman, he is spoken of as 'Brahman' simply on account of his spiritual knowledge. In ordinary life, words are often used based on a future state—as when someone says 'he is cooking rice' while the rice is still raw. Similarly, in scripture, expressions like 'the renunciate gives safety to all beings' use present terms for future attainment. Thus, some scholars explain this passage by saying that the man destined to become Brahman is referred to as Brahman.
Close to the Sanskrit
Or due to human qualification, the Brahmin may be one destined to that state; 'Human beings thinking they will become all' - thus human beings are introduced; and for them qualification is especially stated in the means of worldly prosperity and liberation, not of the supreme Brahman nor of the lower Prajapati; therefore through the knowledge of the lower Brahman accompanied by ritual, having attained the state of the lower Brahman, freed from food, whose bondage of desire and karma is cut off by attaining all, destined for the supreme Brahman, because of the knowledge of Brahman he is spoken of as Brahman. And in the world linguistic usage based on a future state is seen - as 'he cooks rice', and in scripture 'the renunciate gives the gift of fearlessness to all beings' etc., thus here some explain that the man who is to become Brahman is a Brahmin.