It looks like a line was burnt along the division and the top half was then coloured as it looks like the grain continues from top to bottom if you look carefully
Depends who made it. I saw a guy called John Beaver when I was in the US, he has a jig that allows you to mount a chuck at 90 degrees to a bandsaw blade, then he cuts the bowl in two, then glues them back together again. Surprisingly simple when you watch it done!