The array at the end of the struct is not a VLA on the stack. When you allocate the struct, you add enough extra to hold the contents of the array. VLAs on the stack are pretty much universally considered a bad idea, as far as I can tell.
This is not me; this is Protesilaos Stavrou, a well-known and cherished member of the Emacs community. I just watched this video and, since I'm in no position of helping directly, decided to share it here.
What you’re not getting is the conscious part of “conscious decision”. The brain makes the decision BEFORE the consciousness is aware of it. But that’s not how we think we decide stuff; the experience we have is that we consciously choose to do something. The experiment shows that decision is actually made by the unconscious part of the mind, and the consciousness is only made aware of it later, while still believing it was in control the entire time.