Very true... prison is an unnatural situation for males - lack of females - so other instincts would come into play to fill the void. Some more effeminate males would sadly be forced into roles often satiated by females... and due to sexual frustrations males would incorporate sexual desires with displays of power over another as well.
However, in a situation where females are readily available and a male still chooses to be with another male... it may be safe to say he has true homosexual tendencies...