No clear evidence, sorry, you're right. It's only a rumor that is circulating everywhere, I should have made this clear but only realized this now. Another poster above/below noted that it might have been a misunderstanding of the law by Samsung, according to Yandex CEO. Which is also possible of course. (nonetheless, they still shipped unremovable software in a firmware update)

There's so much uninstallable malware on Samsung Galaxy phones that they probably did it of sheer habit.