Almost all engines make their peak HP WELL beyond the torque peak. Maybe you can show us one that doesn't. You could see such a dramatic drop in torque in a very poorly designed engine. But considering that RCV designs engines for purposes greater than model aircraft I think they know what a good torque curve looks like. The intake and exhaust systems are not so critical in model aircraft engines that one would see such strange curve.

The biggest problem I see with your assumptions is that the prop pitches are accurate. Remember he is setting the pitch by eye on a scale. Using a pitch gauge would be more accurate but most modelers don't have one.

Plot the data on a chart and look at it to see if it's realistic. The torque output at 4400 RPM is so far out of line that it's not realistic. The RCV-91CD reviewed by AJ Coholic in Fly RC showed none of this sort of behavior, and even using prop constants to back calculate the HP and torque curves show that torque is highest at the lowest RPM tested. And HP to be highest at the highest RPM tested.

One last comment. You've neglected to use the three blade constants in you HP calculation.