Is the speed gap between hybrids and road bikes less than the speed gap between hybrids and mountain bikes?

I was on a flat bike path yesterday, and riding alongside someone of similar dimensions. He was on a mountain bike in the same gear as me, pedaling at the same pace, but on my hybrid with narrow tires, I was going significantly faster.

A guy came by on a road bike and he was pedaling at the same pace, and shot by me. Later I saw him stopped, asked what gear he was riding in, and he was in the same gear as well. And I lifted his older road bike, and I couldn't tell much if any of a weight difference between it and my hybrid.

So..what gives? Why was the road bike that much faster? It wasn't the tires. Doesn't seem to be weight. I wouldn't think it was wind resistance. Maybe rider angle effect on pedaling power? Gearing? I don't get it.