Lol, It is weird though. I don't know about your hobbies, but I do crazy stuff, maybe not like that but build things out of stuff, I am reasonable with a soldering iron, and a welder etc. I have reasonable general knowledge. But to build a rocket, even as humble as that requires a fair bit of brain matter. Assuming it will work, we haven't even seen his design. So how can you have that level of expertise and think the world is flat.It is a talent. A "special" talent.
I mean, seriously, how many seriously useful documents can you google about building a workable rocket design that would not make mention about low earth orbits and the earths rotation and so much other stuff showing the world to be not flat. What did he do, switch his brain off at the round bits and back on at the rocket bits.
I call fake, or publicity on this one. He can't possibly be serious about the earth being flat. Has to be a publicity stunt with a hidden agenda.