There are two problems – the app has a bug and is incorrectly reporting the bit depth. The second problem (which partly causes the first problem) is that Apple’s code doesn’t report the bit depth. There will be a fix in the next release to report “16” which is what Preview would report. The sensor resolution of the file may be 12 bits, but the data in the file is usually (maybe always) stored in 16 bits because it’s much easier for computers to work with multiples of 8 bits. Sorry about the bug.