this has nothing to do with openSSH and there is no default password for idevices the default password gets loaded when openssh is posted.
the PDF files that hack your idevice can be downloaded directly from the website. Index of /_/
these PDF files can easily be altered to not only install Cydia after jailbreaking your ipad but also install a virus.
The only thing jailbreakme.com does is forwared you to a PDF link. Instead of downloading pdf's safari runs them and displays them in the browser. There is a bug in the PDF reader that lets a program included in the PDF file that is run when a device tries to read the PDF.