I think he's talking about animal and plants that prosper in a region they could reach only due to human intervention (think: trans-oceanic or trans-continental travel).

No, what he's saying is that evolution doesn't always produce optimal species for the environment, if a species is so invasive as to out compete the native species, then clearly _it_ is more optimal than the one that literally evolved there. Meaning Evolution doesn't find optimal solutions unless it has the right starting configurations.

Evolution never finds "optimal solutions" (except by happenstance). It just has to reach some solution that works and allows the organism to survive and reproduce. Optimal-ity is not a factor.

Optimal for _what_? It makes no sense in the context of biological evolution.

Optimal for survival in the given environment. However the worth of solution depends on other solutions (organisms)... Interesting way of looking at the problem.