User blog comment:Dtar/Dragon Force Theory/@comment-31021015-20170112071850/@comment-7418318-20170112075428

It wasn't "always stated".

The only one who ever said that Zeref turned Acnologia into a Dragon was Arcadios and even he said it only as a possibility and not a certainty... at a time when he was trying to convince someone else to go along with his plans.

Even before we got far more reliable information to the contrary, it sounded more like fishing for arguments to convince the other than something he truly believed himself.