I have a feeling that Lee Sedol's single win will be remembered as the first and the last instance of a human victory versus a strong AI in game of go.
There are other strong AIs out there now, Zen and Fine Art. Both are active on internet Go servers. They're still losing sometimes.
But if you mean the last victory against the very strongest, you're probably right.
Yes, by strong, i meant alphago level.
Yes, I got that inpression in the moment watching game 4 last year: "We will never see this again." It remains to be proven empirically but that's why we're here.