Interesting research, but this shouldn’t be a surprise to anyone. Any pattern generated by the human brain (password, lock pattern, PIN’s) is likely to follow a distribution pattern that’s heavily influenced by ease of use and familiarity.
Starting in the upper-left corner of a ‘page’ is natural to anyone in the western world (it would be interesting to see if the same applies in Asian countries where traditionally writing runs from the upper-right), and up/down is a more obvious movement than diagonally.
This underscores the value of biometrics to future security, free from human decision-making – fingerprints, facial recognition, voice biometrics.