"It has become inordinately difficult even to begin to think about constructing a naturalistic theory of the evolution of that first reproducing organism," [Flew] wrote.
Current inability to explain a phenomenon scientifically does not imply that phenomenon's scientific inexplicability.
Professor Flew finds himself unable to explain the appearance of the first reproducing organism, and so he elects to posit the existence of a non-physical universal intelligence that (somehow) produced that organism (and, presumably, everything else). Either Flew has an exaggerated sense of his own intelligence ("If I can't explain it, it can't be scientifically explained!") or else he's lost a step or three in his judgment of the soundness of arguments (or both).
Flew is 81 years old—it's probably not that easy for him to micturate, either.
(Okay, that last bit was a snark, but, hey, I'm bored, and if I don't say something like that every now and then, I'm gonna have to forfeit my log-in name.)
Nor does it imply that all things can be explained by science - or known by science alone - or even detected by science.
Science assumes that matter is the foundation everything that exists. This is an assumption, not proven (or capable of proof) by science. It is a worldview, a metaphysics. It is the essence of of scientism.
Some, perhaps like Flew, convert from scientism, most don't even know they're believers.