Asimov himself stated that, having read about positrons and their (at the time) super-short lifespans, he felt that they were analogous to neurons firing between synapses in the brain. He certainly had no intention of working out a full "theory"!
Data's being a "positronic robot" is derived entirely from Isaac Asimov, more or less as a tribute. Although he never wrote a Star Trek script or was ever involved apart from a single credit as consultant on Star Trek: The Motion Picture, Asimov corresponded and got quite friendly with Gene Roddenberry (also Leonard Nimoy).
Trivial note: Many robots in fiction today are assumed or actually stated to be programmed with the Three Laws, something Asimov approved and was proud of. But, nobody is allowed to quote them in their original wording: that right he retained for himself.