They rely on claims from local NGOs themselves, and don’t verify this information.
Local NGO makes a claim. An international NGO picks up that claim and passes it on to the media. The media then reports it.
Why are the media not being more careful? The halo effect.
This is the idea that NGOs are seen as altruistic and without agenda (in other words, they would have no reason to falsely report the facts).
Similarly, an NGO might have a lobbying agenda, which leads it to report a story in a particular light.
Some local nonprofits can be tied to terrorist groups. When HRW picks up their claims, they are essentially reporting the claims of terrorists as facts.
HRW and AI are not news outlets. However, their work is routinely reprinted by the media.
If NGOs are attacking Cameroon, using the unethical tactic of reporting their claims as verified facts (“news”), then something should be done about it.