Higher frequencies present with lower bitrate files

[Ollekebolleke]

I sometimes get strange effects with some files were physical bitrate is said to be low, but spectrum shows complete different view with clearly higher frequencies present: For example below (160 kbi/s mp3 file):
























When I reencode the file with for example a very high frequency (484 kbi/s ogg), the program shows like below and then it's detects the high frequencies:



Any thoughts?