I'm a strong believer in combatting automation dependence. I revisit the "Children of the Magenta" briefing at least twice a year on youtube. I continually recommend it to others.
But this was a totally reasonable point in the flight to be using automation. It was simply a mistake (not even necessarily a lack of understanding) in operating the automation - pushing the wrong button. Something everyone on this forum no doubt does on their phone at least once a month, no matter how well they understand their phone.
Plus some CRM problems - the FO failed to announce the mode change, or the PIC failed to monitor and doublecheck that action and announcement, or other misunderstanding (maybe the FO announced "Speed" instead of "Vertical Speed," or the Captain only heard "...Speed").
Serious mistakes, especially taken together. However, not dependence on, or addiction to, automation.