Is an aircraft's maximum landing weight really weight, or is it mass?
The maximum landing weight given here is actually the mass, not weight.

In general, the various 'weights' given for aircraft are masses, not weights. i.e. they are in kilograms, not Newtons.

This is simply an extension of our everyday usage. As @mins pointed out, if someone asks your weight, you tell your mass (70 kg or whatever), not the weight itself (~686N).