Answer
If the term "Sankhya Yogi" is taken in the narrow sense, it refers to a practitioner who follows the Sankhya philosophy of Sage Kapila. Sankhya Darshana is fundamentally a knowledge-centric philosophy in which the distinction between the Atman (soul) and Prakriti (nature) is clarified through the analysis of fundamental principles (tattvas).
However, in the Gita, the term "Sankhya Yogi" is not used in this limited sense alone. In the broader sense, a Sankhya Yogi is a yogi endowed with intellect and discernment — one who is capable of comprehending the subtle distinctions between Brahman, the individual soul (jiva), and the world through intellectual analysis. For such practitioners, the path of knowledge (jnana-marga) is naturally more suitable, because the foundation of their spiritual practice rests on contemplation, discernment, and philosophical inquiry.
Traditionally, such knowledge-oriented practitioners have generally taken sannyasa (renunciation) and pursued the practice of knowledge. From this perspective, it would not be inappropriate to describe "Sankhya Yoga" in its broader sense as "renunciation-accompanied Jnana Yoga."
Therefore, it is clear that in the Gita, "Sankhya Yogi" does not refer merely to a follower of Sage Kapila's Sankhya Darshana, but rather to a practitioner whose commitment and devotion are grounded in knowledge and discernment.