The clear thing that makes me believe that MGK may have created a response dis to capitalize IF Eminem came out with dis at him is the absolute FACT "Rap Devil" and "Not Alike" both used the same producer. So it is indeed plausible that MGK did hear the song months before. In fact, Em's song could very likely been done a good minute during his recording sessions with Royce and it may of been something that could of been on Royce's album but Em decided to keep it for himself. Nevertheless, if the producer may of been the one who sorta leaked this song months prior or told MGK directly of it. It is highly likely that was why "Rap Devil" came out so quickly with a video already set to go like a day later after Kamikaze. I don't think Rap Devil ever would of came out had Eminem not dropped his album. It also explains that 3 albums line because it'll been accurate had Em not dropped Kamikaze.
I don't think it is really a FAKE BEEF, but definitely contrived and strategic on MGK's part. He was prepared for it.