He's referring to pedalling technique. Are you using clips? If so, you need to refine your technique so you are at least not creating extra work for your self, but ideally using 2 or 4 stroke pedalling motion. You can think of pedalling in this order:
1. Piston pedalling: Only using the downstroke for power. This is natural for most riders.
2. Improved piston: Lifting your back foot, so that your power stroke is moving the bike and not lifting your other foot. This is how most pro roadies climb.
3. Up and Down: Pulling up with your back foot to use your quads in both directions. Great for BMX.
4. Clock pedalling: Adds the calves in forward and backward shuffles between down and up strokes. Great for long fast flats.
Each is faster and more efficient, but requires a lot more strength and energy as there is less recovery period. All require practice to make the motion smooth. Practice pedalling only on the upstrokes for a while, then move on to pedalling using only the forward and back shuffle motions. Then work on integrating them into a smooth stroke that makes power everywhere. This is mostly roadie stuff (why I know about it), but I'm sure the fast guys in BMX do this stuff. If you piston pedal, you're not using as many muscles in your leg. Those that are strong enough to pedal smoothly around will always be faster. HTH