If you take a look at the history of HBO Max's rebranding, there were several titles removed from the streaming service just right before the change. It's entirely possible, that removal of said titles preempted subscriber decline, or you could attribute it to the rebranding.
I believe a lot remains unseen at this point, and the CFOs comments could be considered valid; that churn and user overlap from Discovery+ could have played a part in the decline.
Not that the article title is misleading, there was a user decline after they rebranded.