I think what he was getting at is that all energy production pollutes in some form. If it's more environmentally friendly, but less efficient it means you have to use more of this more environmentally friendly stuff (that still pollutes) to produce the same amount of useful energy, which still ends up creating the same amount of pollution, it not more.
It's like if something is 99% environmentally friendly, but only 1% efficient, you need may end up needing to produce 100x of that 1% harmful bit to get the same amount of useful energy which is the same amount of pollution as if you went with something that was 50% efficient and 50% environmentally friendly.
"Environmentally friendly" is a rather vague term, when in reality, it's the pollution produced per watt of useful energy produced.