Not really. Drugs do have psychoactive components that can, provably and physiologically, cause addiction with a single use. Opioids famously have been observed to cause neural changes in rats consistent with addiction after a single dosage.

It's more like, gambling. Millions of people gamble, a portion of them have a gambling addiction. Does that mean that gambling causes addiction? well, obviously, yes, but also, no. Or else how to explain the millions of people who can even take a vacation in Las Vegas but don't feel a constant compulsion to gamble all of their money away. Equally, almost every single human being has sex in their lifetimes, but only a small portion of the population suffers a compulsion to have sex constantly. Does sex causes addiction? the question is in itself way too simplistic and disingenuous. Addiction involves so many other factors that it can't be reduced to “being exposed to porn causes addiction”.

I think it's more of a continuum between purely psychological and purely chemical, and most things fall somewhere in the grade.