I suppose it would be a type of "folk etymology", although more specifically "люди бога ведают" seems likely to be a so-called "backronym" or "acrostic" that was later mistaken for the real etymology. The English wikipedia article on "backronym" gives the example of the Alcoholics Anonymous slogan that "the word denial stands for Don't Even Notice I Am Lying". But I assume no one in AA literally believes that the word "denial" originated as an acronym.
Similarly, the popular notion that "fuck" derives from "Fornication Under Consent of the King" or "For Unlawful Carnal Knowledge" was originally a semi-witty joke that some people naively took to be true. So you might call it a "fake-folk-etymology."