If you aren't into the idea of insulating yourself with bird feathers (even if they're theoretically responsibly sourced), you'll be happy to hear that Vollebak's Solar Charged Puffer uses synthetic insulation.
Most synthetic insulation or "synesthetic down" is heavier and slightly less effective than real down (especially the high grade stuff), meaning that you have to use more of it. And indeed, the jacket is quite heavy at 1,650 grams, so it's certainly possible that the jacket is as warm as Vollebak says it is.