my guess is the fact that the "connected/disconnected" notification is "always" on. as the app refreshes the notification, android may be counting them as new. my guess is this a "persistent notification".
For example, i just restarted my phone, and there are no notifications on the Tesla app and the notification for "connected" is not present. After a while, the connection notification appeared and the Tesla app now shows there's a notification.
if you long-press the icon, you should get a small toast menu showing what the notifications are. once i did that, the notification dot went away, but came back again because the notification still exists.
I'm on stock Android 10.