If they succeeded, the manager would have pointed to the feature as an example of their “hustle” and ability to get things done where others couldn’t.
If they shipped the feature and it crashed the website, the manager would blame the front end team for making a fragile system that couldn’t handle a simple feature.
If they failed or were blocked, they’d point out their working proof-of-concept and blame the front end team for onerous process or politics.
The real litmus test is how the company reacts to that manager after this stunt. If the company sides with the hustle manager, it doesn’t bode well for engineering in the long term. When management rewards shows of effort instead of long-term results and fails to acknowledge negative externalities or selfish managers, you breed more of that behavior.
However, if management sides with engineering and shuts the hustle manager down, you’ve found a good workplace.