AcreetionOS Media Writer uses a custom User-Agent header for the AcreetionOS project to have a clear statistic of how prevalent of a download method it is.
This User-Agent string is in the following format: AcreetionOSMediaWriter/$VERSION ($OS $OSVERSION; $BUILDARCH; $LOCALE; $DETAILS).
You can disable this behavior by using mediawriter --no-user-agent which will make it use the Qt default User-Agent string (likely Mozilla/5.0).