Several posters have mentioned a contradiction between the K-50 weight and its body being magnesium (K-50 and K-30 are specified with exactly the same weight). So, one of them must be wrong.
Obviously a web designer doesn't create a completely new page when it is nearly identical to another one (for the K-30). So, the practice is to copy and paste the old page and to add the changes by hand. However, it's very easy to make mistakes, especially when the web-designer is no camera expert.
When this procedure is followed indeed, it is plausible that the specification for the body material (magnesium) is only added when it is a real change.
Moreover, the K-50 body is clearly different from the K-30, so it is plausible that they should have different weights, even when they are made from the same materials.
So, my conclusion is that the presented weight is not correct and that the K-50 body could be magnesium.