Yes, that is exactly what he means.

@endso, you may be onto something. What looks like 'extreme' to us may be 'optimal conditions' for an alien. The so-called extremophiles may well be creatures that found environments they were used to from home.

Only one tiny problem with that. They have the same DNA structure as everything else on this planet, hinting strongly on a common ancestor. I would expect an alien to have some sort of self-replicating, DNA-like molecule at heir core, just like us. It is also highly likely to be carbon based, for reasons I mentioned a while ago. But the chance that it looks exactly like DNA seems infinitesimally small to me.

So no, sorry. Extremophiles are not aliens. They are our own outcasts, bullied by the big boys and forced to eke their miserable lives on the fringes.