Under-engineered, if anything. If they had spent more time on development, a simpler machine could have been built. "Insert your favourite bridge building quote"
You’re right about the colloquial definition but I think the OP is more on point about the crux of the issue. Most physical world engineering applications are about the skill of stripping away as much as possible and still getting the job done. It’s an exercise of working within constraints. “Over-engineering” is ignoring those constraints.
"Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. Now please take away this overpriced juicer."
Definition written by management who can't tell good from bad. Ya see too many engineers got involved I reckon, should done what I told em, keep it simple fellas.