Don't try to read too much into the doc being more serious. I don't think you are but just in case. You never know if he just got the estimate for his boat repair or his wife just informed him her parents are moving in with them or if he just had to give bad news to a patient or what.
It's important that bladder cancer patients report any blood or problems immediately, and that alone is enough reason to be a bit serious with you.
It's how I knew mine was back. They couldn't find where the blood was coming from but it was back. It took a visit to a 2nd opinion doctor at a top bladder cancer hospital to finally find it and when they did it was already invasive.