The system flagged the messages as harmful and did nothing.
There's no mention of that at all.
The article only says "Today ChatGPT may not recognise this as dangerous or infer play and – by curiously exploring – could subtly reinforce it." in reference to an example of someone telling the software that they could drive for 24 hours a day after not sleeping for two days.
That said, what could the system have done? If a warning came up about "this prompt may be harmful." and proceeds to list resources for mental health, that would really only be to cover their ass.
And if it went further by contacting the authorities, would that be a step in the right direction? Privacy advocates would say no, and the implications that the prompts you enter would be used against you would have considerable repercussions.
Someone who wants to hurt themselves will ignore pleads, warnings, and suggestions to get help.
Who knows how long this teen was suffering from mental health issues and suicidal thoughts. Weeks? Months? Years?