This shows som tam prepared in Buddhist vegetarian style: in addition to satisfying vegan requirements, pungent plants in the Allium family (e.g., chives, garlic, onion) are also excluded.
Excerpt from Wikipedia:

Green papaya salad is a spicy salad made from shredded unripe papaya... Som tam, the Thai variation, was listed at number 46 on World's 50 most delicious foods compiled by CNN Go in 2011. The dish combines the five main tastes of the local cuisine: sour lime, hot chili, salty, savory fish sauce, and sweetness added by palm sugar. The ingredients are mixed and pounded in a mortar... In Thailand, it is customary that a customer ask the preparer to make the dish suited to his or her tastes.