No one calls the Catholic Church "a cult", nor do they call, say, Zoroastrianism a cult (to pick a relatively small religion with weird practices).
I will note, if, like me, you're not a native English speaker, that there are two words, "cult" and "sect" that commonly exist in many European languages but often mean opposite things. That is, in English a "sect" is any "flavor" of a religion - catholicism and protestantism are sects of christianity; while "cult" describes closed off communities (usually of a religious nature) that are deemed harmful to their members. In my own native language, the two meanings are reversed - we use "cult" for "legitimate" religions, and "sectă" for closed off harmful religious communities.
See especially definitions 3 and 4.
The article is certainly not using definitions 3 or 4, which simply don't make sense in the construction "sex cult". It's not worship of sex/worship through sex (definition 4), and it's not "a system of religious practices related to sex" (definition 3).