Is bak kut teh a dish that began in Hat Yai?
It is not introduced as a dish of origin in Hat Yai. It is a Chinese-descent dish met in the Songkhla area, and a menu item through which you can learn about the area's varied food culture.
Bak Kut Teh · บักกุ๊ดเต๋
If you want a meal of warm soup on a Hat Yai trip, choose bak kut teh. Pork ribs are simmered with herbs and aromatics. In the Songkhla area it is introduced as a soup dish with a Chinese-style herb aroma. If you eat pork, enjoy it slowly with rice.

The aroma of herbs and aromatics is added to a broth in which pork ribs have been simmered. The colour and richness of the broth differ with the recipe. Alternate between the ribs and the broth to notice the aroma.
The broth uses pork too. If you avoid pork, choose another dish.
Bak kut teh is one of the Chinese-descent dishes met in the Songkhla area. It does not mean that it was first made in Hat Yai. On a day when you want a meal different from crunchy fried chicken, have a meal of pork rib broth and rice.
It is not introduced as a dish of origin in Hat Yai. It is a Chinese-descent dish met in the Songkhla area, and a menu item through which you can learn about the area's varied food culture.
The standard bak kut teh contains pork ribs. If you avoid pork, it is better to choose another dish. Please note that even if you eat only the broth, it is a dish made with pork.
If you want to read more about these dishes and regions, these sources are a good place to start. Ingredients and cooking methods can differ from one eatery to another.
Sharing image credit: Indradi Soemardjan http://www.indrani.net · CC BY 2.5