It has little to do with meditation, it's an ever present tension imposed by simmering-hostile environment that most Russians live in. In the same vein it's a common Russian misconception that Westerners always fake their smiles. They are often genuinely more friendly and chill.

And yes, if you smile too much you are taken for лох, even if you are native. Get to an urban market some day and smile to sellers, посчитай на сколько обуют.