Yes - I have the same intuition. But it may also just be u fortunate timing and obligations. Sometimes companies have requirements from customers to notify them within some time period following a breach.
Like many in the US, I saw this somewhat late. Did the OpenAI disclosure come out first? Did Mixpanel notify OpenAI (due to contractual obligations), who then investigated and ripped Mixpanel out of their systems? And then OpenAI disclosed it publicly, forcing Mixpanel to disclose publicly?