Sure. I take it, though, that even if it's true that brains are computers, it doesn't follow from this that computers are brains; a massive brain may well be a computer, but a massive computer may not be a brain. So, mentioning computers in the face of my scepticism as to whether the relevant collection of things would constitute a brain may not be very helpful - it depends on what one antecedently supposes to be essential to something's being a brain, on which:
I take it you mean to draw parallel between the manner in which, as you say, "Humans communicate, pass ideas ... between each other and incrementally improve on these ideas with each generation", and the activities of a brain. I can appreciate that there's room for a comparison here, but I'd be hesitant to go so far as to say that, insofar as we humans are engaged in the kind of activity that you describe, we collectively constitute a brain (though there might be other things in vicinity that I would find it more plausible to say).
It's unclear to me that there are very strict necessary and sufficient conditions for something to be properly counted among the brains (and - if there are such conditions - it's unclear to me what they are). It might help, then, to treat the notion of something's being a brain as involving an implicit appeal to certain resemblances to paradigms; that is, we can say, x is a brain iff x is the same, in certain key respects, to a suitable paradigm of brainhood (and so, given the variety that one finds among biological brains, it's likely that there will be many different ways of being a brain). Since we're more likely to agree on whether something is a paradigm, this seems a neat way to proceed.
But of course, it's an open question as to what the features of paradigm brainhood might be, such that their instantiation in some candidate object (be it a computer, or set of persons, or whatever) would suffice for a suitable similarity to obtain between the object and the paradigm, such that the former could be properly counted among the brains. I take it that this is precisely the point on which we disagree: while I can appreciate the similarity that you highlight between - on the one hand - a network of individuals, refining certain ideas, and - on the other - a brain, doing whatever it is that brains do, it's not obvious to me that this similarity suffices for the former to be properly counted among the brains.
By way of a hand-wavey explanation: Insofar as it's a biological notion, it seems natural to me to say that brains are things which are the organs of single organisms, responsible for - on the one hand - regulating various physiological functions, and - on the other hand, processing sensory input and triggering appropriate behavioural output. To the extent that it does this well, the organism will - in general - be less unlikely to meet an untimely end. In addition, this (and other) activity in the brain clearly underlies consciousness.
Now, I don't mean to suggest that, to be properly counted among the brains, a candidate object must be like this in all respects, but it does seem to me that some essential similarity would be missing from the case of a collection of persons, sharing ideas. Perhaps this is because I find it natural to think of the brain in teleogical or functional terms - specifically, in terms of the role it plays within the individual organism, and the contribution that it makes to their survival, enabling them to orient themselves in their environment, etc. And so since - in the situation you describe - it seems there's no kind of organism, such that the candidate brain - considered as type - belongs to it, and contributes to its survival (or to that of its members), I'm disinclined to call it a brain.
Still, I take it that none of this actually matters for GoatLord's thought experiment, which could be reposed not in terms of brains, but (with more biological neutrality) in terms of 'thinking things'. The brain is a thinking thing, and perhaps there could be thinking things which - because they don't satisfy the relevant biological criteria - were not brains, but were thinking things all the same. If so, the question could just be reposed in those terms.