Wouldn't be surprised. I mean, just because it's a manga/anime series, doesn't mean they can't advocate awareness for something like that. NAKED APE sometimes does stuff like that. As well I think it might have been The Tyrant Who Fell In Love which had a really strong reference to gay pride month in America (not surprising if it's a yaoi though).
I think it's great, btw, if creators of manga are doing that. <3