Tokyo-Yokohama Information Source

After a long day of travelling around Tokyo showing relatives the beautiful sights of Tokyo, my husband decided to sit down on a vacant seat next to a middle-aged woman on the subway. To his horror, the woman stood up and went and sat down on the opposite side. Why did this woman take that action?
My husband couldn't have been smelling as he washes himself everyday (and he doesn't smell of the horrible green tea which so many Japanese smell of). He wasn't wearing anything "reveling" which could have made the woman uncomfortable. No he isn't "big" either and didn't require the extra seat space. Was this racism or was the woman trying to "make the journey of the foreigner more comfortable" by making more space for him (this reason was given in a Newspaper article recently)? This has never openly happened to us so far (in the past 2 years we have been here) and it was quite a shock. Answers are welcome.