Wikipedia says the term kuai tiao was borrowed from Teochew, a variety of Southern Chinese.
Kuai tiao, written ก๋วยเตี๋ยว in Thai, refers broadly to Thai rice-noodle dishes. The word is traced to the Teochew form guê diao, written 粿條, a term for a type of rice noodle. Teochew-speaking migrants were part of the wider Chinese communities that helped spread noodle traditions across Southeast Asia.
The borrowing is part of a larger regional pattern. Related words appear in Cambodia as kuyteav, in Vietnam as hủ tiếu, and in Malaysia and Singapore as kway teow. These terms are not identical in pronunciation or meaning in every context, but they reflect historical movement of Chinese languages, ingredients, and cooking techniques through the region.
Kuai tiao should not be confused with the name pad Thai itself. Pad Thai is the Thai name of a stir-fried dish, while kuai tiao identifies the noodle tradition and appears in many preparations, including soups, boat noodles, and pad thai. Teochew is therefore the specific Chinese variety requested, rather than the broader label “Chinese.”