I think it is only logical to say that person is gay just from their thought of homosexuality. Person's thought are powerful drive force for their actions. If someone is thinking about homosexual then most likely they will end up becoming one. So having gay thought and being gay is same thing.
Since these are only THOUGHTS of homosexuality, you cannot call the person "gay." If they begin to have homosexual habits, such as excessively kissing another man or showing signs of affection toward another man, they can then be called "gay." But just as well, it should not be offensive. It is simply their way of life.
Having thoughts about being gay, a lesbian, or bisexual doesn't automatically make you gay, a lesbian, or bisexual. If you're having excessive thoughts about liking another gender, then you would classify yourself (loosely) as queer. You can get more specific in certain areas; for example, a person who has excessive thoughts on liking both genders, but is not certain of their sexuality can call themselves
I have thoughts myself but don't call myself gay. If someone thinks something it does make it them that thought. I could think of robbing a store, but it does not make me a criminal. Until you have tried and experimented and mad your choice, you are not a homosexual.