What's wrong with this graph?

The following came from Swivel - Draw conclusion from data.



I looked and thought ... OK, don't really get the data, the article or ... hang on ... which line is which. Is the red curved line "Historical stock prices ..." or is the spikey line "Historical stock prices ..."!?!?!?

Usability: 0/10

[Updated - an hour or so later] Usability has shifted up to 8/10 - they've changed one to blue.