Development and reverse engineering probably takes ~500 hours. They probably won't sell more than 1,000 (I'm making these numbers up). Cost for a small run of boards with component placement, with shipping is probably $20-30. They're probably not making much.

Edit: On the crowdsupply page, they mention "As of today, we’ve shipped nearly 1,500 of them. That’s 1,500 boards manufactured by PCBWay, assembled by Cyber City Circuits, and tested, packed and shipped by me personally, plus 1,500 temperature sensor boards hand-assembled by yours truly." Hand-assembly of SMT components is very laborious and not very fun, so that will add at least 10 minutes per board, which adds another 250+ hours of work.

Well, apparently the person who made it said they can't do another run like the previous as they made zero money off it.

Not zero money; it turned a profit of about $16,000, but it was hard fought. I wrote a detailed post about the economics of the gadget here: https://www.patreon.com/posts/closing-and-on-78683968