I did. I also explained that the place I worked had a very strict policy forbidding any employee from serving as a reference (the only thing we're allowed to do is give them an 800 number to call which will verify employment)

The person I worked with was apparently a really really good friend of the person I was interviewing, so I assume it just came up in conversation, like "Hey, do you know so-and-so. They're applying for a job here."

Amusingly, the guy actually did speak well of me to his friend, he just then proceeded to notify my boss that I was interviewing at another company.

I'm surprised you're so calm about it. I would have been furious!

I was annoyed when it happened, but it was a few years ago, and I try not to dwell on negative experiences. Usually about a day after something happens, I process it and move on.

Also, it tangentially led me to go back to doing technical work, which I much prefer. Having all my responsibilities as a manager removed forced me to decide what I really wanted to do at that point in my career. On the whole, I'd say it worked out for the best.