If someone else is logged onto icloud on my phone would they have access to my text messages?

I'm borrowing my brothers old phone temporarily. We have different numbers, but he was signed into his icloud account on this phone. I was just wondering if he would be able to access my text messages from his ipad that also has his icloud log in information. I realized before I signed out of his account that one of the texts I've gotten sounds very bad out of context, so I just wanted to make sure he couldn't see it. Thank you.