The name “Patañjali” (v. l. “Pātañjali”) has been translated into Tibetan as “Chur lhung,” and it has been recorded in the Mahāvyutpatti (Sakaki, no. 3498; Fukuda & Ishihama, no. 3496). To be sure, the name has also been rendered as “Thal mo lhung” (’Jam dbyangs mkhyen brtse’i dbang po, Legs par sbyar ba’i bstan bcos kyi byung tshul cung zad bshad pa ngo mtshar zla zhun gsar pa’i ’dzum phreng. In Sa skya’i chos ’byung gces bsdus. 6 vols. Beijing: Krung go’i bod rig pa dpe skrun khang, 2009, vol. 6, p. 184.7). The rendering “Thal mo lhung” is acceptable and it does not have to be “Thal mor lhung.” It is comparable to the rendering of “Devadatta.” Both “lHa s/byin” and “lHas s/byin” are acceptable. Ācārya Sems dpa’ rdo rje points out that the Tibetan translation “Chur lhung,” or rather “Chu lhung” (as he has it), is actually a “misunderstanding” (go nor), and he translates the name as “Thal mo sbyar ba can.” See Sems dpa’ rdo rje, mKhan chen zhi ba ’tshos mdzad pa de nyid bsdu ba’i ’grel ba (sic) dpal de kho na nyid gsal bar byed pa’i sgron ma. The Red and Black Crown Karmapa Series 41. [Kalimpong]: Shri Diwakar Publications, 2017 [Tibetan Commentary on Chapters 1–6 of Śāntarakṣita’s Tattvasaṃgraha]. But is the Tibetan rendering really based on a misunderstanding of the meaning of the name “Patañjali”?
Not being a Sanskritist, it is not easy to dig Sanskrit sources that explain the name “Patañjali.” But a quick online search reveals some interesting information associated with the etiology of “Patañjali.” According to one, Ādiśeṣa, the Nāga king, who is the bearer (or even emanation) of Viṣṇu, who was seeking a mother, fell into the handful of water that Goṇikā, a woman who was praying to the sun god to bestow her a son, had scooped up to offer, as the handful of water was the only gift she could find. The veracity of Patañjali’s etiology is secondary, but the Tibetan translators and their Indian collaborators who translated “Patañjali” most probably knew Patañjali’s etiology and hence translated the name as “One Who Fell into the [Handful of] Water” (Chur lhung) or “One Who Fell on the Palms [Filled with Water] (Thal mor lhung).” I, for one, do not think that the Tibetan translators misunderstood the name “Patañjali.” This case is very much comparable to the Tibetan rendering of the name “Umā” as “dKa’ b/zlog ma.” Ācārya Sems dpa’ rdo rje’s translation does not seem to account for pat or pata. With regard to the etymology of the name, Mayrhofer, after considering some speculations, states: “Alles recht ungelaubhaft.” See Manfred Mayrhofer, Etymologisches Wörterbuch des Altindoarischen. 3 volumes. Heidelberg: C. Winter 1992–2001. Cf. MW (s.v. patañjali): “fr. pata + añj°?” This speculation or suggestion is not found in the PW.
In short, we repeatedly realize that Tibetan translators, when they did translate proper names, did not always follow what seemed to them their literal meanings but considered their etiological backgrounds. So it seems it is necessary to do some background study before we conclude that the Tibetan translators misunderstood and mistranslated certain things. By the way, as Ācārya Sems dpa’ rdo rje rightly points out, the Tibetan translation of the title Tattvasaṃgraha should not really be De kho na nyid bsdus pa as if we have Tattvsaṃgṛhīta but should rather be De kho na nyid bsdu pa.