Personally I don't believe that even from Zack himself. He's still knee deep in with Netflix, the last thing he's going to do is let the internet go wild that he is coming back to WB. That's not professional towards Netflix. There will be a time and a place once his Netflix stuff is done.
Sure, I could be totally wrong. But people ask, and he has to give some sort of answer. Celebs say stuff like this all the time and do a 180 months or years later, it's simply too early right now. Looking at it a different way, perhaps WB really haven't contacted him yet, but they are aware of his contract and that is why ?? Maybe they want to get their plan together first before contacting directors for stuff beyond the immediate next films.
WB would surely have to consider Zack further down the line though. I mean it would be free marketing and "huge" marketing at that. Can you imagine the internet if they simply announced Snyder. It's be huger than Cavill. Plus all the actors would be totally for it.
But like you say without Zack playing some role further down the line I'll also be somewhat disinterested.