Well firstly, I was also talking about the struggling gay kids who see their hero say that ABOUT THEM, not just the people who might follow in his footsteps. The influence of this kind of thing can go a lot of different ways.
How do you think homophobes are created? Or racists? Or PETA activists?
It's usually a series of influences, parents, media, heroes that shape a lot of what we think and how we act. Folau's words alone won't make a homophobe, but they could contribute to an idea that becomes homophobia with other influences. Little Billy McRuggerFan thinks that these gays must be bad if Izzy Bloody Folau thinks they go to Hell, and that helps make little Billy more receptive to homophobic ideas.