If you go to the link, they carefully define fluency levels. It appears that there are three classes of languages when analyzed as to how difficult it is to learn to both speak and read them for a native English speaker. The easiest class of languages (mostly romance languages) takes about 600 hours to achieve fluency. The second class of languages takes about 1100 hours and the third class of languages takes about 2200 hours.
Thai, like the majority of languages, falls into the second class. However, it has an asterisk next to it, meaning that it is a bit more difficult than most languages in the second class. But it is not nearly as difficult as Mandarin, Korean, or Japanese, for instance.
So, according to this chart, it takes about twice as many hours to achieve fluency in Thai as it does to achieve fluency in a romance language.