I don't know what you mean by the "step-down nature of the converter" at 5:58 because moving the de-energizing coil to the secondary side of the coil made the transformer a "step-up transformer", did it not? This is the way it appears to me, as omitting the de-energizing coil would make the transformer neither step-up nor step-down, but rather an isolation transformer, would it not?
So, the forward converter is a step-down (assuming a 1:1 transformer ratio) because it behaves like a buck converter (with the classic input-side demagnetizing). We can intuitively verify this by observing the voltage on the L1, D3, D5 node to be a square wave with amplitude = Uin and duty cycle < 1. Once we move the demagnetizing winding to the output, it becomes a forward and flyback combined. This makes it potentially a step-up.
Sure, just remember that the forward converter usually takes a maximum duty cycle of 50%, so you'll get less that 0.5 times the input voltage at the output.
