When he wrote the article, an IC had about 30 components. He said he had realised that the complexity over the next 10 years would go from about 60 components to thousands on a chip.
He said he didn't expect Moore's Law to be precise, but his prediction turned out to be more precise than he expected. In 1975 he looked at what had happened and saw that several factors accounted for this growth. Participants in the semi industry reckon they have to move along at this sort of rate or fall behind technologically.
Moore's Law has become a self fulfilling prophecy he said, and he was personally amazed at the way things had panned out.
Answering questions, Moore said the law would extend for another 10 or 20 years, but that wouldn't be the end of the road. The engineers will have billions of transistors to make the design.
Intel got hold of the 1965 article after the Ebay auction it launched and sent us a copy. You can read it in PDF form, here. µ