Quite some time ago, my husband did a language exchange with a Japanese woman in her mid 20s. This is a "classic" arrangement that most Japanese people dream of where both parties speak English for a designated time and then they both speak Japanese for an equal amount of time. I say it's a "dream" because it's a rare situation where a Japanese person can practice English without paying for it.
The arrangement was never really all that satisfactory for my husband because the Japanese woman did little to correct his speaking whereas she had all the benefits of an experienced English teacher. She also tended to ramble on at a level of Japanese which was too difficult for him to benefit from because the vocabulary was too high level and she spoke too quickly. Essentially, she just chatted away without making any adjustments or efforts that might help him gradually build his level.
Before he this arrangement ended, she told us a story that gave us pause. She had been corresponding with a foreign man who was in his early 50's and married. When I say "corresponding", I mean real letters, not e-mail. This exchange happened before the internet. I can't recall exactly how she got to know him, but I believe it was not through an initial face-to-face contact, but rather through some sort of pen pal organization. I do remember though that he received her letters at an address other than the one he and his wife resided at. It was also unclear whether or not the wife was aware of her husband's correspondence with a much younger Japanese woman.
During the course of the English portion of the exchange, the woman told us that he was visiting her in person in Japan and that, when they walked around Tokyo, they held hands. We asked her if he did anything more intimate than that like kissed her or hugged her and I believe she said he did hug her hello, but not much more than that. Both my husband and I told her that we felt the circumstances of their arrangement and the fact that most adult Western folks don't hold hands unless they are romantically involved or trying to keep a hold of a child suggested that he was after more than just a friendship.
The woman rejected the scenario we suggested was being played out and said he was simply a nice man and the hand-holding meant nothing. To this day, I'm not sure what became of her relationship with him or, for that much, what became of her. She moved to Yokohama after awhile and referred us to a different language exchange partner (who was actually more unsatisfactory and eventually my husband terminated the exchange with her). We never talked to her again.
In Japan, one thing you can't help but notice is that adults hold hands noticeably more often than they do in the U.S. Adult women in particular will hold each others hands on occasion in casual (non-romantic) situations that you wouldn't see adult women doing so back home. I can't say though that adult hand-holding between males and females is common. Usually, you only see it between those who appear romantically-interested in one another or have what looks to be a parent-child relationship. Given this, I do wonder why my husband's former language exchange partner was so sure the older fellow's intentions were free of romantic interest.
I've never discussed this topic with students or any other Japanese person, but I do wonder if Japanese women in particular are more comfortable with certain forms of physical contact between women. Somehow, I think two women holding hands back home would make people instantly think they were lesbians whereas it doesn't hold that connotation in Japan.
Another reason I believe they may be more comfortable with women touching other women is that, on more than one occasion, I've witnessed or been told about one woman playfully grab another woman's breast. In fact, there was once a Japanese T.V. commercial where a woman lost weight and her friend was shown visiting her for the first time since she'd slimmed down. The formerly chubby woman had retained her larger than average breasts and lost all her weight in her stomach, hips and thighs. The first thing the friend did was remark on how shapely she was and poke her finger right into the other woman's breast. Foreign women (including some of my former coworkers) teaching in Japan also have had their breasts grabbed by women they were teaching, though, fortunately, I have not been one of them.