I think the problem is that when you declare someone who is bisexual as gay, you are defining them by their attraction to the same sex. Your definition neglects the fact that bisexuals are also attracted to people of the opposite sex, which just as significant and important to their lives. However, so far you have been actively dismissive of this attraction to the opposite sex saying they are gay and also happen to have sex with women or are attention seeking. It may not have been your intention, but it comes across that if a bisexual man is in a relationship with a woman it is somehow not genuine and is instead a pretence.
Do you not see how hurtful this could be, and why they may feel the need to speak out to defend themselves from such accusations? In a way you are denying one aspect of their identity, just as politicians legislating against gay rights deny them another aspect of their identity.
Also I looked up LUG in wikipedia, because I'd never heard the term before. It seems it can be used as a derogatory term against bisexual women. It made me realise that people who are bisexual can potentially be subjected to hostility from both gay and straight people.
Edited by Malcolm, : No reason given.