Is bak kut teh a dish that began in Hat Yai?
It is not presented as a dish that began in Hat Yai. It is a Chinese-descended dish you meet 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 with warm broth on your Hat Yai trip, choose bak kut teh. Pork ribs are simmered with herbs and aromatic ingredients. In the Songkhla area it is introduced as a broth dish with a Chinese herbal aroma. If you eat pork, enjoy it slowly with rice.

The aroma of herbs and aromatic ingredients is added to the broth of simmered pork ribs. The color and richness of the broth depend on the recipe. Alternate between the ribs and the broth and notice the aroma.
The broth uses pork too. If you avoid pork, choose another dish.
Bak kut teh is one of the Chinese-descended dishes you meet in the Songkhla area. It does not mean that it was first made in Hat Yai. On a day you want a meal different from crispy fried chicken, have pork rib broth with rice.
It is not presented as a dish that began in Hat Yai. It is a Chinese-descended dish you meet in the Songkhla area, and a menu item through which you can learn about the area's varied food culture.
The typical bak kut teh contains pork ribs. If you avoid pork, it is better to choose another dish. Please note that even the broth alone is a dish made with pork.
If you want to read more about the food and the regions behind it, these sources are a good next step. Ingredients and cooking methods can differ from one place to the next.
Sharing image credit: Indradi Soemardjan http://www.indrani.net · CC BY 2.5