Confusing compiller error message when [`FnOnce`] closure moves captured ownership-value out of self

Hi! I'm trying to understand the compiler error, see some ambiguity here. Perhaps it's just a language issue. English isn't my native. If I run the example from the link above, I get the error: closure is FnOnce because it moves the variable bob out of its environment. I also tried to simulate the closure to better understand what's going on, because, in my opinion, moving ownership of the captured variable to a variable declared within the closure body isn't so obvious. I'm confused by ...