I mean, this is also a particularly amateurish implementation. In more sophisticated versions you'd process the user input and check if it is doing something you don't want them to using a second AI model, and similarly check the AI output with a third model.
This requires you to make / fine tune some models for your purposes however. I suspect this is beyond Gab AI's skills, otherwise they'd have done some alignment on the gpt model rather than only having a system prompt for the model to ignore