They only mean that the quantity of power you and their other customers consume will be less than their “green” energy production capacity.
Moving electrons are fungible.
Okay, now I’m worried. We just put a vintage neon sign in our kitchen. Is this a problem?
I don’t know. Is it?
Potential issues are the sign interfering with your wi-fi, making your radio signals go to crap (especially if you listen to AM), stuttering or slow frame rates on your TV, reduced cell phone range or an increase in battery usage as the phone cranks up the power levels to cut through the neon sign’s interference.
If you haven’t noticed any issues, then it’s not a problem. 
Neon signs don’t put out significant UV or X-ray radiation so as far as I’m aware there is no health risk either.