Assuming this is on an android phone with the normal Google Play Services on it then you should expect that Google can theoretically read anything that appears on it. It’s probably not that sinister though, I don’t imagine anything is being sent away and logged (though it theoretically could be!), there’s probably just some process which reads every incoming notification and if it thinks it sounds like a task then it offers you the prompt. Is this some setting you haven’t disabled in Google Assistant?