@Kim Shook This dish, among many others, is very easily customizable. In fact, many times, when you order this in a local food place, it won't have any chili in the dish at all, but will have a dish of chili on the table for you to add as much as you want. I've found that Viet food is not usually very spicy - there are a lot of flavors, but tongue-tingling, make-you-sweat heat is not usually one of them, unless you add tons of chili yourself.
ETA: There are actually no chili flakes in my version either... when I marinated the chicken, I used a bit of chili paste, but that paste isn't that hot, but has a good chili flavor. And I put a bunch of thinly sliced "spur" chilis - long hot red chilis (that aren't that hot) in the dressing, but I defanged them so their mild heat was even milder - my wife is not a huge fan of very spicy food. But they have great flavor other than heat, which is why I put them in.
