> When people refer to VK being a clone of Facebook

The 'clone' label comes mainly from the fact that the site was originally a copy of FB right down to the colour scheme. The two sites have diverged significantly since then, of course, but if you'd removed the logos and presented the two sites to someone in the first couple of years, they would have been hard pressed to pick them apart.

VK is also remarkably popular in Russia, etc, because of the massive amounts of copyrighted music and film material stored on the site that Durov steadfastly refused to remove. It helps with your popularity when one of those 'many features which FB does not have' is an unlimited stock of pirated content accessible for free....