It was a (half) joke about GLaDOS being attractive to lesbians for specific reasons, and cishet men not really getting it. But also, I don't care if it's a "fan theory?" The character is like, a complete blank canvas, so I think it's kind of silly to say she isn't queer because it isn't like, "part of the lore."
GLaDOS also has pretty specific character traits that are easy to fuck up if you don't understand why they're endearing, which is more of the point.