As mentioned before, it is only a joke. In Norway it's rare that あなた see two boys that have such a close friendship as Didrik and Alex has. They often touch each other and hugs and stuff, and if somebody in Norway sees that, they will be shouted " gay! " after. we all know they aren't gay, but would it really matter if Alex was gay? He would still make awesome 音楽 and be a wonderful person.
Did あなた also know in Russia a magazine wrote that he was gay? And あなた know what he did? He LAUGHED and JOKED about it. Why? Because he has a LIFE, he DOESN'T care. he isn't weak as a feather who runs crying saying " those mean girls called me gay! ". He knows that people joke about him, hell, did あなた know he actually joke about himself? WOAH!
As far as I know is that some girls just joke about it. Personally I don't like that joke cause talking too much about it every time when they see him with a boy is sick. I don't wanna offend anyone but it is tiring to read it everywhere.
I would say a lot of people say this (which is not true) Because,some people think he looks like a girl because of his eyes and might be also the fact that his voice is very soft....or the best reason...those people who 発言しました this are just jealous :)