I think you're misunderstanding. The reason people are theorising that Iron Bull might be bisexual is because his description says that he'll will jump into bed with "anyone" rather than using a specific gender like "any woman" or "any man". The fact that he's a man-wh0re is a moot point.
This is true but I think people are taking it from: anyone since it's not from any woman and I think there is many people who want to romance him as guys. So I don't think many are: he sleeps around a lot, he must be bisexual! , they might be just happy cause this means he is sleeping with people and it doesnt' seem to be gender limited from that text. If that makes sense. I think quite many people are tired of stereothype in DA with bisexuals being very sexually active.
The thing is we are not sure. I should not be dampening peoples excitement and speculation ofc. Gosh I love making stuff out of almost nuffink myself. Guess this is just a thing that annoys the hell out of me and so I act really pricklish. 
It might be that they are not ready to reveal all LI's and all sexualities. Therefore they are using the phrasing "anyone" instead of gender specific.
"He overeats, drinks himself sick, and will hop into bed with anyone he’s reasonably sure he won’t break."
He overeats, drinks himself sick, and will hop into bed with any woman he’s reasonably sure he won’t break.
He overeats, drinks himself sick, and will hop into bed with any man he’s reasonably sure he won’t break.
How would you rephrase that to make it "neutral" without revealing his sexual preference? 