It is my opinion that the chlorine dioxide was used up when it contacted the stomach lining and stomach fluids.
I ran a test on 2.5 g of mucous a while back. I added 200 ml of a solution with around 500 PPM available chlorine dioxide and a little over 60 PPM free chlorine dioxide in it. I had about a 98.6% loss in chlorine dioxide immediately upon contact.
I don't know how much mucous there is in the stomach lining, but it is reasonable to think that a 10 ml solution would be used up in a similar fashion.