I had something similar happen last month on a MUP. A cyclist decided to reenter the path verrrry slooooowly from the opposite direction I was heading and crossed the width of the path equally slow. Meanwhile super speedy tri guy was coming up behind me. I brought my speed down and was preparing to go around the cyclist by staying on the right. Super speedy tri guy blasted right past me on my right side with barely any room to spare. If I didn't have a mirror I probably wouldn't have expected anyone to be there and a spectacular collision would have been the result.