Spoiler ahead, make sure you've read the side arc with Byakuya!
So you know how the end goal is to get to the moon and see who's broadcasting? Well what if the robot from the side story got the radio signals from Senku and others and found out what happened to cause the stone age? And then he's broadcasting those suspicious messages so that he can meet Senku?
Yeah. Frankly we don't know how many people are revived on Earth. After listening to all the radio waves from those people, maybe Rei understood something. And now he's broadcasting weird messages from the moon bc there's something really important there Senku must see, something ONLY Senku must see or know. That's why it's in Senku's voice? Bc when reading the side story I don't think Rei landed on the moon, but he did circle it. And I bet he would've noticed anything weird going on and investigated it. So I think Rei is the one that's on the moon.
Nuuuu second male syndromeeeee ╥﹏╥
And it is quite severe as well. ╥﹏╥