It's a very complex topic, but to put it as succinctly as possible, the key difference is between self-declared atheists who truly appear as such, and those who insist on their atheism, but various quasi-religious elements are nevertheless clearly discernible in their lives and worldviews (to the point where I would dispute whether it makes sense to exclude them from the general definition of "religion").

Overall, my impression is that among the atheists found in North America, those of the latter kind are far more frequent and prominent compared to the post-Communist Eastern Europe, with Western Europe being somewhere in-between, but closer to North America. (Of course, these large geographical regions contain parts of greatly different religiosity, but what I write tends to be true for the local atheists found there regardless of their percentage in the local population.) Why this is so, and what exact quasi-religious elements are commonly seen among different sorts of self-declared non-religious people, are complex and fascinating questions, which are however difficult to discuss because they touch on many ideologically sensitive issues.

When I read people's writings on all sorts of issues, I can usually discern the two types of atheists pretty quickly and reliably, and based on your comments I've read in this thread and elsewhere, you do seem to belong to the true sort like you declare. Assuming you're writing from somewhere in Europe or the Anglosphere, as most people here are, this by itself places a significant probability on you being Eastern European, and more specifically from one of the less religious EE states, like Hungary, Czech Republic, or various former Soviet republics (as opposed to much more religious places like Poland or Croatia). Considering that your username is the word for "piglet" in several (but not all) Slavic languages, one of which is Czech, this seemed like a high-probability guess. Also, some additional evidence is that your English is excellent but still a little bit Slavic-souding, and your writing has a slight and vague quality typical of Central Europe that is very hard to explain. (By the way, if you're curious, I'm Croatian.)