The “4.4.38” is from the actual source code version. Within the “.config” file, the suffix is from the “CONFIG_LOCALVERSION”. This is one of the few options which are safe to directly edit with a text editor, but the menu config editors also make this available (I forget where, one of the general options near the top). Example:
FYI, if you were to copy the “/proc/config.gz”, gunzip it, and rename it as “.config”, then it is an exact match to the running system’s config…other than CONFIG_LOCALVERSION.