Fortunately, he sent a note to the team indicating where the test would be running and referencing the problem he was trying to show was fixed. So I know something. From there, I had to figure out the answers to my questions.
And it occurred to me, this is what we do for our customers. Given a problem description and a location (for logs or whatever), can you figure out what's going on? We have questions about what the system has been doing; can we get answers to those questions?
Sure, I can wait until tomorrow or send an email - after all, the tester has the answers about what he was doing. But with a customer that's not always possible; sometimes customers simply don't know the details of what their customers are doing. In the end, the definitive source of answers to my questions had better be the system itself. Any other source is going to be less available.
If I have a question and the system cannot answer it, that's an opportunity to improve the system.
Of course we rely on multiple sources of information. Those sources of information change, though, and some are more reliable than others. Ultimately, you can rely only on the things you can control - your system and its logs. The rest is just something you hope you can get - probably available, but not guaranteed.