The biggest criticism I usually see of this narrative is that the British and the French may have also seen Thailand as a neutral buffer zone between their respective empires. By staying out of Thailand, they reduced the risk of conflict between them, supposedly.
I have no idea how valid this idea is, or how much of a factor it would have been, I'm not a historian.
Rather as this history describes, the Thai monarchy and government appears to have modernized (Westernized?) just in time to be able thread a needle between two empires, playing them off each other to maintain independence.
It is worth noting that the word "Thai" has come to mean "free" in the eponymous language. Thailand literally means "land od the free".
Note that this history conveniently ends before World War II.
--
I have to ask, though, where are you getting the idea that ไทย ("Thai") also translates to "free", or that it's pre-WW2?
Google Translate doesn't list that as a translation for "free" at all, and thai-language.com mostly lists that in the context of the Free Thai movement ([a WW2 anti-Japanese resistance](https://en.wikipedia.org/wiki/Free_Thai_Movement)).
There's probably some subtleties I'm missing, but it really seems like a niche definition.
I confess my ignorance in this specific matter, but when somebody leaves something on the table it means that it costs too much to take it.
Of course the reality of nation state politics is complex and there's never going to be a single "true" theory.
My suspicion here is that the buffer theory takes agency away from the Thai and makes it seem like just luck, while this article does the opposite, and the reality is probably a big mess somewhere in between those.
It is by no means a given that Britain and France would see a need for a neutral buffer zone given that the home countries of the two powers only had a small channel separating them in Europe. They'd be used to the idea of sharing a border. We can all but guarantee that both of them had people looking at the map every so often and asking if it made sense to officially add Siam to the imperial holdings.