User blog comment:Miskos3/Fairy Tail Episode 245: Tartaros arc: Hell's Core, Review/@comment-26537859-20150808124600/@comment-25111584-20150808133653

@Nick: Mashima is known to collaborate closely with the anime though. The KotSS arc was supposed to be completely different, but it was rejected by Mashima. The Erigor fight in OS arc is also something that he said he had to cut out in the manga. And, finally, he drew up the rough plot for the ECS arc too (for all the hate that we throw at the anime team, right? XD).

So ... this might be something of Mashima's too. Not saying it is, but definitely not impossible.