How did you wire it up? The PI runs at 3.3v and the Arduino runs at 5v so I assume you ran it through a converter. There is one example on the web where someone ran it though a CD4050. See the page here Raspberry Pi and Arduino via GPIO UART | andremiller.net
Assuming you did not directly connect them I am unsure what these values are supposed to mean. They aren't ASCII values because they are larger than 8 bit chars (values > 255).