There are several methods for creating a Thai adverb and (like most Thai grammar rules) the rules are rather fluid. There’s usually more than one way to make the same adverb and which way it’s said will probably depend on how it flows with the rest of the sentence. Think of how we say both: “It’s simple!” and “It’s easy!” Both mean the same thing, but we’ll choose the one that flows best with the sentence or situation. It’s the same in Thai, so don’t be too concerned about it.