It seems to use a history depth of 5, both for you and it. So it creates a 'fingerprint' from your past 5 moves and it's past five moves, and then picks what is the most winning move in it's history given that same fingerprint.
That strategy seems to work reasonably well, I tried to just go all paper for a while and it responded with all scissors. Ouch.
Seems like it would act exactly as you've just described no?
Edit: Ok re-reading your initial post I think I misunderstood you. However it still doesn't explain how it could pick up the pattern quick enough - there are 3 possible responses each time, so until it's tried all 3 responses it won't know which is best given the fingerprint. However it will pick up the pattern by the 2nd cycle.
I think it's using a more sophisticated learning strategy than you suggest.
But once it builds up a database, I imagine that is far more effective.