It seems there is a light shining from the direction of the camera in the second (ISO 6400) image, thus it seems brighter.
Btw, as the 5D Mark II shoots 21MP pictures, and the one you showed is only 0.7MP, the noise is of course not missing.
PS:
The EXIF data shows a flash being fired, thus the light I described.
{
ColorModel = RGB;
DPIHeight = 72;
DPIWidth = 72;
Depth = 8;
Orientation = 1;
PixelHeight = 682;
PixelWidth = 1023;
ProfileName = "sRGB IEC61966-2.1";
"{Exif}" = {
ApertureValue = 3;
ColorSpace = 1;
CustomRendered = 0;
DateTimeDigitized = "2010:03:29 05:17:24";
DateTimeOriginal = "2010:03:29 05:17:24";
ExifVersion = (
2,
2,
1
);
ExposureBiasValue = "1.333333";
ExposureMode = 2;
ExposureProgram = 3;
ExposureTime = "0.04";
FNumber = "2.8";
Flash = 16;
FlashPixVersion = (
1,
0
);
FocalLength = 16;
FocalPlaneResolutionUnit = 2;
FocalPlaneXResolution = "3849.212";
FocalPlaneYResolution = "3908.142";
ISOSpeedRatings = (
6400
);
MeteringMode = 5;
PixelXDimension = 5616;
PixelYDimension = 3744;
SceneCaptureType = 0;
ShutterSpeedValue = "4.625";
SubsecTime = 89;
SubsecTimeDigitized = 89;
SubsecTimeOriginal = 89;
WhiteBalance = 0;
};
"{JFIF}" = {
DensityUnit = 1;
JFIFVersion = (
1,
1
);
XDensity = 72;
YDensity = 72;
};
"{TIFF}" = {
Make = Canon;
Model = "Canon EOS 5D Mark II";
Orientation = 1;
};
}
