Interior walls upstairs

Finished wall upstairs, made from plasterboard with a metal (aluminum?) structure. I think at one stage the builder would have liked these walls to be concrete block like the downstairs walls. I am no sure why I think that or why he would prefer it.

Perhaps they would be stronger and provide better sound insulation. Concrete is better (although not easier) to drill into than plasterboard / gypsum (or is it gipsum? Or gyprock? I'm still not sure what the difference is, if any) as long as you don't mind using wall plugs.

And I'm not 100% sure why he ended up using plasterboard. Concrete block is much heavier so I think the most likely explanation is that it was better, structurally, to use gypsum. These interior walls are not on top of any load-bearing walls downstairs so maybe the design meant that concrete block was not an option.

In this photo you can see the skeleton of another interior wall. It would be nice to remember where these metal struts (there must be a proper word for them?) are because they are useful for drilling into if you need a strong structure to screw into for some reason, e.g. to hang a shelf that will have heavy things sitting on it.

The photo also shows the finished bathroom floor, which is about 10cm above the level of the rest of the upper floor. This is because we did not want a wooden bathroom floor.