some confusion here? Wheelies involve pedalling, Manuals don't.
I've been riding BMX and Mountain Bikes since 1981 and the 2 tricks are very different, regardless of the type of bike. its not about whether you are sitting down or not?
you can wheelie on a BMX : on which you can't sit down on unless you are a midget, because it has a 12" seat tube, 1" of seat post extension and a hard plastic seat, this does not stop you pedalling...
you can manual on a BMX: its a back wheel roll with no pedalling or brake involved, you are not applying power to the drivetrain
-wheelie is combination of pedalling, and rolling using weight shifting to maintain the balance point
-manual ROLL is never pedalling once you enter the manual, but simply rolling using weight shifting to maintain the balance point
there is no pedalling during a manual roll, otherwise its not a manual ROLL but a wheelie. The rolling is the hint really, and the key to a good manual. too much rear brake is cheating when your balance fails, and will often stop a manual because you will loose too much speed.
here is a hop to manual roll:
manuals are one of the most fun tricks on a BMX when you have the skill and experience to take a manual roll around the landscape of an entire skatepark without stalling, needing to pedal or brake
if you really want to know about manual rolls check out Mike Aitken's section in the older "Etnies. Grounded" bmx film