I’ll trust the calibration code. at a glance, it looks legit, and I don’t feel like running that. there’s no way to get that wrong and not have it blow up spectacularly, and that didn’t happen. by the way, for monocular intrinsic calibration, the object points of the checkerboard need no scaling.
I’m seeing a good variety of poses for the board… without oblique poses, the focal length may have a huge margin of error, but you’ve got those, so it’s not that type of issue. and the squares, in proportion to other identifiable objects, look close enough to 21.8 mm.
pictures are 720 by 480. guessing the field of view from the pictures, that would make me expect the 626 focal length to be true. 1130 would fit a 1280 by 720 camera better, or a camera with narrower FoV (zoomed in).
can I assume that you don’t zoom or scale at any point, neither optically nor digitally? did you take the calibration pictures in a different way from the pictures for pose estimation? webcams have “modes”. still mode and video mode may have differently sized crop regions of the sensor data.
the size of the (3D-printed?) target looks plausible too, in relation to your fingers. maybe someone stretched the ruler?