Is it common for a managing editor of a University Press to solicit book proposals from PhD students at a conference? I am a PhD candidate in the very early process of writing my dissertation, and I'm presenting my first chapter at an international humanities conference soon. I received an email from the managing editor of a well known University Press that was impressed by my topic and wants to meet to discuss possibilities. How common is this? 

Is it quite common for University Presses to solicit meetings with PhD students? Or is this a rare opportunity? His interest was so unexpected (because I always assumed you approached editors if you wanted to publish) that I'm not sure if this is a promising opportunity.

So how often do managing editors of University Presses solicit authors that are ABD?
I interned at a university press, and it was common to go through conference programs and identify interesting topics/papers written by PhD candidates/early-career scholars. It sounds like it's a little early in the process for you, but it is definitely worth taking the meeting.