Here is the link to an article I read concerning it:
Yes, I think there is a grain of truth in this article. From what I can tell, "fake it till you make it" is not a very popular approach in Russia, and you don't have to smile at everyone when you in fact are feeling miserable. It's a bit different for service workers now, but still not to the degree when a cashier in a supermarket has to smile at you and ask "how are you doing?" *shudders*. I honestly don't understand what's so wrong with "smileless" politeness so to speak, in my opinion it feels better when you know that the person you're speaking to is not secretly hoping you would just stop bothering them so that they could stop holding a "proper" smile. Still, I wouldn't say we don't smile at all, personally I smile a lot and so do many of my friends, it's not that different from anywhere else really. It's just that it's not obligatory, and when I smile I usually mean it (hope it makes sense).
Now, is it not acceptable to smile at strangers in Russia? No, I wouldn't say so, but I think you should keep in mind that some people indeed may interpret it as something really personal. But I'm not sure it's the case in Russia only, I remember smiling at one audiobook (and, by coincidence, at one guy sitting in front of me in the bus) in another country, and he interpreted it a sign of flirtation as well. So, I don't know. Maybe it wouldn't be the case in the US, for example, but I'm not really sure.
Mostly this article is true, especially for elderly people. However, globalisation influences Russia too, many international companies apply standards of smiling for customer service and sometimes it looks very funny.
It doesn't mean that Russians don't like to smile and laugh. We really love good jokes and laugh a lot with friends.