When interpreted as an unsigned integer, it actually corresponds to the maximum value of almost 4 GB (0xFFFFFFFF). Note that the fields are declared as SIZE_T, which is unsigned. (Not sure if they always were.) The installer may be incorrectly assigning the value to a signed integer type.

The actual behavior of GlobalMemoryStatus is a bit more complicated, see https://ftp.zx.net.nz/pub/archive/ftp.microsoft.com/MISC/KB/....