It's an effective advert if the purpose is to increase awareness of fire safety. We have some awful ones in the UK with partially burnt teddy bears and stuff. I think it's more leveraging popular imagery to deliver that message, rather than expressing LGBT support.
You can see on the right of the image there is another progress flag with text on it. I think it's safe to say this image is framed in a way to eliminate the context.
Fun fact: "the heat death of the universe" refers to the death of heat, not death from heat. Heat itself will die. There will be no more warmth in the universe, everything will end in cold and dark and ice.
Kinda? All energy will dissipate until everything is the same temperature. Idk what that temperature will be but it might be pretty cold. But heat won’t just, like, go away. It will homogenize.