It's true, but it's user-controlled so it's optional. It will cater to both groups:
1. The group of users who have short questions and long answers--or for whatever reason wants to see more of the answer box than the question box or vice versa--can resize the boxes to suit their preference.
2. The group of users who have wildly varying question and answer sizes and for whom this feature is not useful won't resize.
The resize widget is very muted, so most users won't even notice it until they look for it.
That said, the "Single Box" option is very good, it's just that it doesn't show the separation between question and answer, which looks a bit confusing:
https://i.imgur.com/z7k8kQh.png