“computed height or auto” should be “computed height of auto”

And second: I think you got the explanation wrong why transition-behavior: allow-discrete; is needed when display: none; is involved. It seems in Chris’ article the part that switches from display: none to display: something was omitted or at least I didn’t see it, but as far as I understood it, the style or code that sets it would switch the property immediately, so we would never be able to see a closing animation of height. With transition-behavior: allow-discrete; the actual switch to display: none takes effect only after any animation / transition has finished. (And it behaves the other way around when a style changes an element from display: none to display: something.)
The @starting-style is needed because as you have mentioned an element with display: none ends up being renderd with a computed style of height: auto regardless of the property set to height: 0 via the style. Unintuitive yes, but probably ancient, spec’d, established browser behavior.
Which would mean that we would attempt to transition from auto to auto which will do nothing. Hence @starting-style { height: 0; }.
And third: thank you for the article.

CSS Grid Can Do Auto Height Transitions

So be careful out there on the edge, folks.