This version is 32-bit, but it has 4 cores @ 1.2GHz and 4GB of RAM. Also, it is actually open source, meaning that all the electronic design files (made in KiCAD) are available on GitHub and as soon as we have decided on the correct formats the same will be true for the mechanical/case parts, so you will be even able to 3D print replacement parts.
I could not find the design files for Pinebook so I'm not sure what is "Open Source" about it? Schematics are not sources.
I don't know how you can sustainably make a laptop and sell it for $100. I'm selling the first developer models for EUR 549/599 and I'm not making any profit on these, it's basically passing on the material cost. I guess it's a tradeoff between cutting enough corners to bring the price down and trying to achieve some base of quality and durability. These are different goals.
Anyway, I'm happy to see more activity in the ARM space as that means more eyeballs on ARM Linux applications, potentially more issues filed and bugs fixed.