They are wrong.
Just because you didn't get enough information to reproduce and/or fix it, doesn't mean it's not there.
But, it does mean there is nothing you can can do about it. (Obviously try to get clarification and more info, etc. this is assuming you were not able to.)
Nevertheless, in the back of your mind you should try to remember the bug and maybe you'll come across something that will let you figure out what it was.
This doesn't scale so well for OSS projects, but if it's paid work and the bug came from your client then you better track such things, even if you can't immediately fix them.
On one side, I have trouble getting information out of people ("It had an error" ... "What did it do?" ... "I don't know anything about computers, so I clicked okay. Can't you just fix it?") and on the other, some of the people I report things to aren't willing to even try to reproduce bugs ("I need 8,000 different files, screenshots, etc. of the bug in action, which will require you to shut down production for an hour" ... "Can't you just look at the code for X? It fails every time with the same behavior." ... "No, I really need you to waste a lot of time on this because I'm way too busy to implement any kind of logging." ... "No wonder you won't let anyone else have access to your bug tracker. Something tells me it's a sticky note or whiteboard based system.")
I completely understand how people can fail to report enough information to give anyone any hope of finding the bug, but it's frustrating when you know you've got a good bug report and the developer doesn't want to listen to you.
They're both a list of steps taken to get to a point in the system.
This one? http://imgur.com/jacoj
That'd make an awesome poster.