It's possible Channel 4 only managed to get the broadcast rights and Netflix has exclusivity for streaming/on-demand.
It does sound like it. I have seen a few news articles suggesting this, but nothing definitive:
"But according to Den of Geek Netflix still retains the same rights to Discovery, and is still able to release new episodes the day after they debut in the USA. Presumably they still plan on doing this, because they paid a goddamn fortune for those rights and it would be stupid not utilise them. It's unclear what that means for Discovery being on All 4."