It sometimes happens. I recently read a post on the UBC maple forum about the same unusual branching, but I don't have time to find the thread.
I suppose it's similar to some samaras in groups of 3 or 4 instead of two as usual.
I suppose that itwill disappear next year on new shoots. Maybe a virus or something similar what produces "witches brooms".
If you think that could be interesting, you could take cuttings later in the season, A. buerger. are easy to root from semi-hardwood cuttings, and see what happens...