Trainer resistance question

I've had my resistance on my trainer set at probably a harder setting than it should be, you should see my tire, but lately I've been working on RPM's and consistant pedaling here in my base phase. So, today I let some resistance off and much to my surprise, my speed went up. Is this somehow a false result? How is this? Please be kind, I'm not much of a science or math person and can't figure out how if my resistance is lighter I am using less force so I should be going slower, right? Or am I looking at it wrong?

 I'm not complaining that I'm going faster, I'm just wondering how it works!