Here's the (link) source for Arthur C Clarke admitting bisexual experience. I think it's pretty clear. 
http://playboy.com/magazine/interview_archive/arthur-c-clarke/arthur-c-clarke-4.html
Here's the quote: 
'PLAYBOY: Have you had bisexual experience yourself? 
CLARKE: Of course. Who hasn't? Good God! If anyone had ever told me that he hadn't, I'd have told him he was lying. But then, of course, people tend to "forget" their encounters. I don't want to go into detail about my own life, but I just want it to be noted that I have a rather relaxed, sympathetic attitude about it  and that's something I've not really said out loud before. Let's move on.' 

If you read the entire interview the topic of sexuality is discussed in greater depth. Given the context of the article, I think you've been a little harsh on other editors on this issue. Of course I have to agree that nothing should be added unless properly sourced. I think this qualifies.