Some users just want to turn it on and have it work, and they don't care to know all the technical details. They're the ones who wouldn't understand anyway if you did tell them. You know that glassy look in their eyes when you try to tell them - again, for the umpteenth time - what a networked drive really is? Why even bother?
Then there are the ones who are somewhat computer savvy, but their real expertise is in their "real" job, and they know it. They realize that when it comes to IT issues, they're only about a 3-4 on a scale of 1-10, but they like to understand how things work a little better. They want to know what's going on, but only because they don't want to find themselves dead in the water if I'm not around, and if they "kinda understand", maybe they'll be able to surprise themselves by being able to figure out something on their own. These are usually the kind of users that I may ask what it is I can do to make their computing lives a little better.
Some users, the real dangerous ones, think they know everything about everything. (And as we all know, no one knows everything about everything.) These are the ones who want to know every little detail so they can share their expertise on the issue, and explain why the initial failure was someone/something else's fault. If it's a problem that was obviously his/her fault, I'll explain the whats and whys the problem because I love the look of egg on the face of someone like that. If it's not their fault, I won't tell him/her anything because it's fun to see them wondering, but not wanting to expose their true ignorance.
Then there are the ones who always "imply" that any failure is obviously a failure on someone's part to prevent it, someone other than themselves, of course. These are the ones on whose computer I always find (yes, I may help it along a bit) an unauthorized program, or that "spyware", or that "mysterious" virus that is only spread by email, or something like that - regardless of what the real problem is. They fall into the "egg on your face" category, but a little more fun.
Some users are really nice about everything, but they themselves did something to screw it up. They need an explanation of what went wrong so they won't do that anymore. These are the one's I'm really nice to because they're always really nice to me.
Now in your case, where a department manager wants to know what happened to another user's computer, I might have to know the reason he/she wants to know. Is he/she looking to place blame for the failure? (Either on the IT department or the user.) Most vocally opinionated people are that way because they want to prove their own prowess or deflect blame to someone/something else. I don't know the exact answer to your particular circumstance, but it appears that if you can put this person in the "egg on your face" category a couple of times, he/she may be less "opinionated" in the future.