What is each of their prior probabilities for this setup being true? Bob, knowing that he was selected for his unusual results, can pretty happily disregard them. If you win a lottery, you don't update to believe that most tickets win. Bob now knows of 100 samples (Al's) that relate to the prior, and accepts them. Bob's sampling is of a different prior: coin flipped, then a specific resulting sample will be found.

If they are both selected for their results, they both go to 50/50. Neither one has non-selected samples.