I must reiterate, I don't doubt Terence's abilities, what I doubt are repetition of borderline mythical tales without extraordinary evidence (albeit,I accept someone might say Terrance is the extraordinary evidence).
sure, we have many attestations of speed reading too, and of course there will be attestations of people trying to sell a particular child or education method (or indeed scam).
And I've seen some very convincing performances (and yes, 2 year olds can pick up some basic symbolism, recognition, and repetition). but they lack the ability to comprehend or extend past their specifically repeated contexts. if you film only the contexts of their true positive successes, you can almost sell it, but their errors in extension to anything but rote quickly reveals their comprehension of what they're capable of shouldn't be confused with literacy/numeracy.
different issues abound with attempts to measure or quantify IQs in the extreme ranges at all, let alone in children for which there will be almost no standard applicable method, and it's interpretation is even dodgier.
I mean, another cynical man might say, obviously someone who has lived a life like Terrance must have been given remarkable opportunities. since he clearly did not introduce himself to the gifted study at age 3, and given that we do not have standardised testing at such an age someone was likely a driving force behind him in his youth. the obvious candidate would be his parents, who partake in strong educational and repetitive training, but in the context of the pedagogy of Australian education of the time, would also have to had a very strong narrative needed to overcome some of the dominant "hold them back" attitude of the time.
I mean, we see the same thing with Beethoven and the like. everyone is so focused on the prodigious properties of the person in their later life, critical thinking and skeptical inquiry tends to go out the window. we want to explain greatness through some inherent difference, rather than say the alternative: maybe Terrence is great because of some innate ability. but primarily it is almost certainly the opportunities afforded to him via his circumstances combined with the work and practices and momentum of his parents and his family and then in later life, of himself.
relatively non-scientific hocus-pocus like "taught oneself to read at age 2" literally would go against almost all knowledge of language or child development theories. yet otherwise intelligent people accept such old wives tales without much critical thought.