I don't suffer from social anxiety, but large gatherings such as the one you describe irritate me because I am sensitive to the noise and bustle (especially the din). The longer I attend the event the worse it gets. If the possibility existed, I might very well do as you did, and stay outside the main group.
I had to attend many such gatherings in a professional capacity, and in such cases it is important to undertake your avoidance as discretely as possible so as not to appear excessively outside the "group". I mainly did this by forcing myself to be present for key moments, and then leaving or getting off to a quiet place. If you knew there were going to be group introductions, it probably would have been wise to join your group for the short while that your introduction was taking place. NT's are quite keen on this group/team concept and in my experience it is best to play along to a certain degree. If this happened on just one occasion, though, I wouldn't worry about it. If someone mentions it, just tell them you had had a really stressful day and were decompressing.