The news comes from Heroic Hollywood's Umberto "El Mayimbe" Gonzales, who was a guest on the Collider Heroes video cast. Around the 10 minute mark in the video below, Gonzales and the hosts are discussing what Marvel's recently announced 2020 mystery movies may be. Moon Knight is mentioned as a possibility, but Gonzales says he's heard they're preparing the character for the "back door pilot" treatment on Netflix, similar to the Punisher in the second season of Daredevil.
Gonzales doesn't say much more than that. Rumors and speculation about Moon Knight coming to the MCU have been circulating for a long time, without anything really solid to hang the idea on. It's unclear if Mayimbe has heard new information about the project, or if he's referencing older rumors.
Either way, he's right about Moon Knight being a much better fit for Netflix than Marvel's big screen. Moon Knight is often referred to as "Marvel's Batman," and has the dark tone and history to match. He'd fit right in with the vision Netflix laid out in Daredevil.