Why does Twitter think this image "may contain sensitive material"? (pic)

I re-tweeted a Positive Life (Positive life are here in Sydney) tweet about PrEP; that is, taking Truvada to avoid HIV infection even if the sex is unsafe. It has in the last while become a powerful weapon against HIV infections.

Yet because there were two men in it the message was distilled down to a risky post I guess to click on, with a warning about what you may see upon viewing the media.  This can only reduce the effect of the message as people steer away from wanting to do so.

FFS it's just 2 guys. Upon seeing the warning message most people would think it was going to be porn! In fact the same message appears in a gay porn message complete with video and all. Why is this innocent photo, obviously nothing more than a header for the post, included in that?

BTW, apologies for no links to twitter on this. The internet here has been mostly offline all afternoon (yes we're in eastern Sydney in 2017).  Thanks Turnbull for fucking nothing.......