You're getting downvoted while being right. A dark pattern is tricking the user. Not saving the data they enter. But most people around here call anything that is distasteful a dark pattern.
It's not tricking, but it is deceptive since they haven't chosen to submit. The current mental model of forms are to save data entries when you actively submit.
Yes, there are some settings panels that automatically save changes, but I have never seen it for forms.
If there's an submit button on that form then that would be an even stronger signification to the user that nothing will be sent to the servers until you click that button.
It is a dark pattern - it tricks the user into thinking their data won't be submitted until they click "submit," but instead saves it right away. It would only not be a dark pattern if the form clearly said "your email address will be uploaded to our servers immediately after typing it."
Why were they tricked into thinking that? OP didn’t mention any text stating that. Lots of sites send updates constantly, I’ve never been tricked into thinking they didn’t I just wasn’t explicitly informed. Which is a difference.