Isn't this the key point, though? The answer to that question depends entirely on the context of your relationship with the person asking it.
If a client calls me up and asks how my day is going, the socially acceptable answer is "It's going great, thanks!" with the addition of some remark about the weather, that one is looking forward to the weekend (if it's a Thursday or Friday), etc. My client doesn't really care about my day, they're just asking because it's a social nicety. (They probably do care to the extent that if I break down and start sobbing, or there's just a choked gurgling sound at the other end of the phone, then they may well not get their money's worth that day...)
On the other hand, if my wife asks me how my day has been, I can reply honestly and candidly - though, again, if she's busy or she's had a bad day herself or she's asking this question whilst spooning food into my son's mouth, maybe I will temper my response accordingly.
An understanding of these sorts of social niceties based around context is something that the socially-aware take for granted and, clearly, the author of this article and people like him find very difficult.