I've never found any evidence for this. Even Takayuki Tastumi, one of Japan's leading cultural critics, didn't find any cross-cultural influence between the two in his academic study on cyberpunk cross-cultural influences in his book Full Metal Apache: Transactions Between Cyberpunk Japan and Avant-Pop America (Post-Contemporary Interventions) .
It's just something people like to say, I suppose. Probably because both authors are talking about similar things and have familiar content but, as seems to be the case, most are likely unaware that Gibson and Shirow began publishing their popular works at approximately the same time.
They both started publishing at the in late 1982 and early 1983 respectively, just a few months apart from one another. Not enough time to be influenced by the other due to translation barriers. (Just to put this into perspective, it took 2 whole years for translators to translate Neuromancer into Japanese).
Meanwhile, Masamune Shirow's first work, Black Magic M66, was about an A.I. and an android. Does that mean when Gibson later wrote about A.I.s he was influenced by Shirow?
I don't know. I'm inclined to think not. In all probability, they most likely arrived at their ideas independently of one another and were writing about similar technology that just hadn't been defined as a genre yet.
We call it *cyberpunk* today, but regardless of who influenced who, both men remain true visionaries.