It's "32GB", but really 32,000,000,000 bytes, or whatever, using powers of 10, not powers of 2. So when it's formatted it's actually more like 29GB, and then the system takes up some of it, so you are left with about 25GB.
More here.
32GiB = 29.8GB - so they're using a definition that whilst correct is a bit misleading.