I am equally impressed by your ability to find offence in a mere factual statement.
Fact: Few women are kernel developers.
Fact: Gays are men. (Hint: The female ones are called lesbians. Gender neutral term: homosexuals)
Considering this, why do you think it offensive if a male dominated group is (clearly as a joke) described as "gay party"?
Do you not like gays? Do you not want to be associated with them? Do you think being gay is offensive to others? ;-)
BTW: The gay parties I have been at looked quite different to this picture... :-)