This came from the esafety commission not from the executive, the commission has separate powers and is free to enact them. And yes in Australia they are seeking to de-escalate political tensions that could arise from sharing the material, such as copycat violence.
Further: Initial notices warned social media platforms that footage of the stabbing was illegal 'Class 1 material' and should be removed immediately.
Class 1 material is content that promotes or incites violence or is likely to cause offence to a reasonable person.