Played preliminaries with a Gold V

My duo partner is telling me that I only got placed in gold V because he was gold V to begin with and when he played with me, his ranked MMR was given to me. Is that true? This was my first preliminaries and he only played with me for the first one. I went 8-2. How does it work, do I actually take his MMR. Is there any way for me to reset if this is true because I want to work up the ranks myself.