Al is special because he has been selected to meet Bob regardless of what he observes. Therefore his data is genuinely uncorrelated with how he was selected for the meeting.

Not quite. He was selected to meet someone like Bob, in the sense that whoever the messenger was, he'd have seen 25/100 big. He didn't know he'd meet Bob. But he regards the identity of the messenger as irrelevant.

You can bring out the difference by considering a variant of the case in which both Al and Bob hear about Charlie's plan in advance. (In this variant, the first to see 25/100 big will visit Al.)

What is the relevance of the fact that they observed highly improbable event?