Things are getting a bit recursive now. This thread was discussing the ethics and legality of the phenomenon of paying influencers to plug products in the first place. The article is about exploiting that phenomenon.
That said, the accounts in the article are fake, yes, but they claim to be real. That's not fiction, it's fraud. If they had set up the accounts to clearly state that they are fictional characters, and still gotten paid to endorse products, then it's a lot more like product placement in movies.
(Hmm, I wonder if you could actually pull something like this off. Most major social media celebrities do appear to be fairly highly engineered personas, the leap to pure fiction doesn't seem to be that big)