The Sheets

First, let me say I have really smart kids. I don't say that to brag or toot my own horn. They are just all smart in school. I am blessed, I know. This is the reason I am always so dumbfounded when they do something absolutely dumb. Today was one of those days...
This afternoon, I gave Carsten his set of sheets, told him he needed to change sheets and bring the dirty ones upstairs. He disappears for a little bit and then runs past me with his dirty sheets on the way to the laundry room. Awesome I thought, he did it without complaint or me having to remind 3,000 times. I was almost in awe. Later, I went upstairs to put on the next load of clothes and became confused. In the pile of sheets Carsten had brought up were cream and white sheets. If you know me you can probably guess that I do not mix-match sheets. So I dig deeper to find the bottom sheet is still folded in the pile of "dirty" sheets along with 2 of the three pillowcases.
Apparently Carsten thought I wouldn't notice if he only changed the top sheet and 1 pillowcase. REALLY!?!