If the protagonist is gay, is it a gay novel?

This is obviously a photo of two young cowboys wooing Annie Oakley. Perhaps. Or, Billy the Kid giving a tip of his hat, asking the handsome young buck for a dance. Depending on your predisposition to an image, it could be either. Or neither.

A good friend reviewed my debut novel set a century in the future and said she doesn’t normally read LGBT fiction but really enjoyed the book and the main character. I got five stars. Friendship certainly had nothing to do with it. So the protagonist in The Chronicles of Spartak–Rising Son is bisexual and the other main character is gay. A few known straights are there too but for most it is unclear and unimportant to the story. Like in most books. And, hopefully, in real life too.

So it is a LGBT novel?