"One could easily turn this example into a function that casts an integer to a pointer, and then cause arbitrary memory corruption."
No, one couldn't! One has contrived a program that hardcodes precisely the condition one wants to achieve. In doing so, one hasn't even demonstrated even one of the two predicates for a memory corruption vulnerability (attacker control of the data, and attacker ability to place controlled data somewhere advantageous to the attacker).
What the author is doing is demonstrating correctness advantages of Rust using inappropriate security framing.
