The capsule sends a signal to the machine that records pH and time, so there is a record. Ask the doctor, or the place that did the procedure. I'll bet it fell off early. Waiting 6 weeks is ridiculous.
Was he asleep when it was placed? It's hard to get the thing pinned to the wall of the esophagus. And that's what they do - pin it right to the tissue. It takes 45 seconds to get it placed right.
The stomach isn't going to be putting out alkaline fluid. The esophagus is supposed to be neutral, about 7, although some put it at 4 - 6. Below 4 is generally considered to be reflux, from what I've read.
Expelling the capsule depends on how fast the person's system works.
I wouldn't be surprised if they try to tell you the test was a failure so there are no results. I'd ask what results there were. I don't believe nothing was recorded, since you saw the numbers. The test could have been a failure because not enough results were recorded, but have a frank discussion with the doctor about repeating it. How old is the child? As a mom, not a doctor, I would think twice before putting a small child through this again.