Either way this looks pretty sheit for Toyota quality. I would contact your dealership and ask about lack of keeping you informed of your car. Not sure how much of that would pose a threat as its hard to see what is exactly involved or what the extend is. That leads me to my next thought process. Bring it in somewhere to have the entire underside inspected and get documents on that severity. I would take that back to dealership that just did the service and also contacts Toyota. This rust issue with Toyota is unacceptable and them not telling you is criminal in my honest opinion. Do you carry any kids in your car? That’s another speaking topic with your dealer and how importantly safety is to you. Yeah I’m overly critically but them not saying anything or documenting it gets me peeved.