Is autodidactism a feature that can only be possessed by special kinds of individuals?
I'd recommend checking out Wikipedia's article on autodidacticism for a start. This might give you a better sense of the context surrounding the word, and whether it really means so much as you feel it does. My first impression is that this is not much more than a semantic issue (but I have a second impression, which I'll get to next). The literal definition seems to be, "A self-taught person," which isn't very interesting. In this sense, of course you are. That's what you're describing: self-teaching.

My second impression is that this is interesting inasmuch as self-teaching is actually rare. That seems odd to me; in what sense doesn't everyone teach themselves to some extent? If we interpret it instead as "primarily self-taught", then I could see autodidacticism being rarer. People usually find educational systems guided by others preferable (or mandatory, as is the case in the USA), but maybe not in a situation such as you describe (whether it's true of Brazil in general or not). When educational systems provided by traditional, mainstream, or public infrastructure are poor, it seems quite likely that one would opt to take advantage of other educational sources as you have. In the past decade or so, the internet has been particularly instrumental in providing this option globally.

I get the impression that using others' educational materials (including syllabi) for otherwise self-guided education doesn't violate the generally intended meaning of autodidact. A stricter definition might limit it only to learning through direct experience with life, but it's hard to imagine anyone short of a feral child fitting this definition truly enough. If an autodidact can learn through contact with others and their guidance and still be an autodidact simply because one has pursued education independently of structured guidance in the form of a professional relationship with a particular teacher, then I agree, it's not that unusual. If it's a question of whether you're primarily self-taught, that might be unusual, but it's not unique. Your particular circumstances seem especially likely to result in such a choice. The ongoing advent of internet-based educational resources makes it more likely that people will "teach themselves" in the same way you do, though it's an interesting semantic issue to consider whether this is truly self-teaching when you're taking advantage of structured lessons provided by others without their knowledge. It seems likely to me that the term "autodidact" itself will begin to lose its meaning in this evolving context of freely, globally available information. In any case, if autodidacticism is at all unique now, it seems unlikely to remain that way.