Someone said, “3 people are fluent in toki pona” What does that even mean? It means squat.
The gold standard of fluency is native fluency, which kids get for free. It is not so free that a language learned as a child will be excellent– for example, if you learn Spanish in the US from your grandmother, you will not speak it as well as someone who learned it in Mexico and took 12 years of schooling in Spanish.
There are about 5 cases of kids becoming fluent in a conlang, ghostlang or other similar language that previously was spoken by no one and is now spoken by them and their mom or dad. One for Living Latin(1), Hebrew(many), Esperanto (many), Klingon (1), Volapuk(1) and a lady on FB who is teaching her diary language to her kids. In the cases where there was only one– obviously they stopped speaking it as adults and probably don’t speak it all that well now. Still, these cases are what linguists prefer when looking for fluent speakers and if warmed up, they might speak it better than anyone who knows that language only as an L2.
Near native fluency is fairly hard to gain as an adult– it happens, but usually there will be accents and grammatical peculiarities in the speech of someone who has learned a language as a 2nd language, even if they are crazy smart. Typically it takes 10 years of living in a country, speaking your 2nd language all the time before you hit near native fluency.
Below that, is a huge range of degrees of fluency. I can converse in Russian, but can’t write it to save my life. I can read Icelandic, often better than I can read Russian. I can pick out a few words here and there in French and Spanish and my translation score would be better than a machine that chose words at random [secret: that's how google translate works;-)]. There are people who can write or read just fine, so long as they have a reference grammar and lots and lots of time. There are people who can spit out a stead stream of words as fast as you like and are generally intelligible, but they make grammatical errors and have a thick accent. And so on.
When I used to organize study groups, ideally everyone is at a similar fluency level. In practice, it turned out that there are 100s of distinct levels of fluency– people that know 100 words, or 1000 words or 10000 words– each case is an entirely different situation. This is why people who each speak English as an second language understand each other better than if they have to speak to a native English speaker. If everyone is drawing on the same 5000 words and same few dozen grammatical constructions, communication is simple and fluid.
People who have never studied a foreign language, nor a conlang, have no clue about any of this. So they hear that toki pona has 3 fluent speakers and they don’t realize that that factoid is bullshit. It is accurate to say that there are zero native speakers, zero near-native speakers, there are 50 to 100 people who have ever written a paragraph or more of toki pona and probably about 10 or 20 who can do it without warm up *right now* (everyone else would probably have to review and re-remember it all).
Also, another important point is that conlangs are not fully defined. You can learn all there is possible to learn about toki pona (and with more effort) about Klingon. And you’ll hit a wall, after which there are statements whose grammaticallity can’t really be judged for lack of native speakers, except maybe to get a ruling from the creator or relevant “language board”.
**NB technical note, there is at least one theory about Tok Pisin– that it was a language of mostly adults and developed it’s unique grammar among adults and then kids copied their parents. This compares with the other story that adults speaking new languages (creoles and conlangs) are in fact mostly using their L1 grammar and L2 vocabulary while the natively fluent children speak with the vocab and grammar of the new language.