It is not magic.

It is isolation plus time plus natural selection — the fundamental mechanism of evolution operating in a specific context that produces a specific result.

The fact that Roraima’s rocks are ancient adds an additional dimension.

The longer the isolation has persisted, the more time there has been for evolutionary divergence.

If the tepui summits have been ecologically isolated for tens of millions of years — which the geological evidence suggests is plausible, though the specific timing is a matter of ongoing research — then the organisms on them have had tens of millions of years to diverge from their lowland relatives.

That is sufficient time for genuinely deep evolutionary divergence.