Looking for Help Recreating Auto-Updated Visual Artboard from a PSD Template

I probably worded that title really badly but I'll try to describe.

A few weeks back I was given a template file for doing some advertising website takeovers for a games website. In the file were a few Artboards, including a Visual Artboard with the website mockup that showed how the design of Artboard 1 (and 2, 3, etc) would look in place on the website.

After a while I realised that as I updated, say, Artboard 1 (and perhaps after saving the PSD, I don't recall), the 'visual' Artboard (i.e. the Artboard that showed the finished design on a web page mockup) automatically updated with the design from Artboard 1. I never output Artboard 1 - never hit Save as... or Export As... but Visual Artboard was updating it automatically as I went.

"Neat," I thought. "I'll take a look at that feature when I'm not so busy."

But now I'm not so busy, and I cannot find how to achieve that magic. Was it a dream? or is this achievable? I wonder if there was a script or something - but surely that's something that would exist in my Photoshop rather then come from the template I was using.

Anyone know how to do this?