Exactly, you cant. If you're having to specify that you lean mostly a certain way then there has to be something propping you up instead of fully falling. If not its the equivalent of me saying that i lean gay but don't like girls at all and I'm not bi, and in fact i only like males.
Sometimes i feel like straight guys assume you need to meet a quota to be called bi, like you're sexual attractiveness to the same sex has to be just as high as the opposite sex. Which obviously isn't the case, Being sexually attract to just one person of the same sex is enough.
In Connors case, like someone else has mentioned, I think his reasoning will be something completely trivial, like this is just his way of saying that he's really only sexually attracted to girls but maybe if a guy came around and he somehow found an attraction there, he wouldn't be apposed to it. Which, if thats the case, he could just say he's straight, it doesn't have to be that complicated.