I would have stopped once I confirmed the leaked keys were valid. Looking at what types of data you had access to wasn't required. Downloading plaintext passwords of other people is probably too far. Impacted users may need to be notified about a breach. If needed, create an account of your own and target only that. If there was a pentester agreement, safe harbor, or other protection that's different. Be careful out…
I'd argue that it was absolutely necessary to gauge the severity of this misconfiguration and furthermore, that Chattr.ai must contact every affected user, not MrBruh.
Their configuration allowed anyone to create an account and access plaintext passwords. There is no telling whether and how many outside of this disclosure have previously accessed this information and may intend to use it. This was negligence of the highest order, and it shouldn't be on the one finding and reporting this issue to rectify it.