Any sufficiently advanced technology is indistinguishable from magic.What can be made of that?
First of all, notice that this is essentially a statement of religious faith, which might seem odd given his many dismissive statements about religion. Clarke's assurance partakes very much of "the substance of things hoped for, the evidence of things not seen", because when one points out that today's technology is readily distinguishable from magic, the response would be to nod gravely and point out that today's technology is not "sufficiently advanced". In fact, Clarke never saw "sufficiently advanced technology"; on Earth, at least, it has never existed.
But surely we can extrapolate based on what has happened over the past two centuries or so? After all, the first human flight was only about 230 years ago, in a Parisian hot-air balloon; the Wright brothers made the first flight in 1903; and Neil Armstrong first set foot on the moon in 1969. During the same period, we went from mail to telegrams to telephone to emails and texts; we saw the development of silent movies, "talkies", TV, and the Internet. Surely this shows that anything that seems impossible or "magical" today can be done with enough technology?
No. Although technology has enabled us to do things that might have seemed possible, but mind-numbingly difficult, science has placed restrictions that were not known before. In 1783, when the first manned flight in a hot-air balloon was being made, it was not known that perpetual motion machines are impossible. Then in the 19th century, the laws of thermodynamics were discovered, which make perpetual motion machines impossible. In the 20th century, a several new things were discovered to be impossible -- distinguishing one electron from another, moving information faster than the speed of light, and simultaneously determining an electron's position and velocity with arbitrary precision, for example.
In addition, there is a real difference between saying that a sufficiently advanced technology could do things that would look like magic to someone not accustomed to it, and saying anything that happens in a story about magic -- that is, anything that a human being can imagine -- can be done with technology. This latter situation would have to be the case, though, if Clarke's statement, as it is usually understood, were to be true. (I suppose an alternative interpretation would be that sufficiently advanced technology would only work about as often as magic. It certainly feels that way sometimes.)
So, for example, a computer with Internet access does indeed act in some ways like the Wicked Witch's magic mirror. The restrictions on a TV, however, are very different from those on a magic mirror or a crystal ball. A TV cannot see what's happening elsewhere without a camera in the right place; a TV cannot see the future; a TV cannot contact the dead.
Likewise, we can now fly, but not at all like superman or even a witch on a broom. It requires pretty big, obvious machines to fly; even the jet backpack, which really only works for short distances, is pretty clumsy, obvious, and limited -- much more so than the descriptions of magic found in folklore.
So to recap, although things achieved by technology today might have seemed like magic in years past, the things magic is described as having done still seem like magic today, and there is no reason to believe that this will change.
What did you expect? Arthur C. Clarke was a science fiction writer, not a prophet or sage. His quote about technology and magic is not really true, but it can be the premise or inspiration for some entertaining and thought-provoking fiction. That will have to be enough.