It is recursively changing the angle at random and shrinking the size. I dunno if that would count as a L-system, the wikipedia article for L-system has too much math that I don't understand
Track down a copy of "The Algorithmic Beauty of Plants". The last time I looked, it was available as a free PDF, too. I think it's a great introduction to L-systems.
I got it when it was first released and spent way too much time poring over it and generating imagery on my decrepit old computers.