Article without the paywall: https://archive.ph/XGz1E
Any service that allows access to content with only a URL carries the risk of being indexed by Google and other search engines. Other less-friendly bots will find it too.
It just takes one person posting the link somewhere public, even if it’s a bad actor with access to their mailbox or chat.
At least OpenAI stopped attaching the account name by default, but allowing authenticated links would be better.