(1) This is a decent estimate for a completely commodity product (Bluetooth headphones). No iOS/Android app development, no content development, very little custom firmware or electronics development required. (That correspondingly means you face the least differentiation and the most competition.)
(2) This is for a "plastic and PCB" product build. That's as simple as it gets. Any product that goes beyond a PCBA inside a plastic enclosure is usually going to have significantly greater design and engineering challenges, not to mention COGS costs. Moving parts? Temperature? Water? Cameras/lenses? Sensors? etc.
(3) The marketing / customer acquisition cost is either ignored or assumed to be some laughably small number. Even at its highest, this article assumes $3/unit customer acquisition cost. That's ridiculous (go look at Fitbit or Gopro or any other filing statements). If it were true, a lot more people would go ahead and get that initial capital to make their own Bolt-o-Phones.
(Disclosure: co-founder of a hardware startup https://www.pantelligent.com/ and about to ship our first production run.)