I don't think this is the case. Isn't it that "guy" is essentially gender neutral in this context? In the same way you can reasonably say "hi guys" to greet people of any gender.
"Silicon person", "silicon gal" etc would be weirder phrasing. "Silicon specialist" maybe but I don't personally think any of this merits discussion.
Maybe it's used neutrally in greetings (e.g. "Hi guys,") but when referring to someone specific, if you say they're a guy, it will generally be assumed that person is a man.
You're right, people do use it neutrally in greetings, not just maybe. And in more than greetings, more as a general form of address. More specifically, I would say that when not used to address multiple people in the second person (i.e. when saying "you guys"), then the word "guy" implies that the referent is male.
Except for idioms like "I've got a guy" where you just mean you've got someone in mind. And that's where I was coming from with "silicon guy" or "hardware guy", "software guy" etc. Just as generic terms for your goto person in those fields, no gender implied.
I hadn't heard anyone use the word "guy" like that before now, and didn't know the word was used like that, so I wasn't thinking of those cases. If you said "I've got a guy" or "software guy" I'd assume you meant you had someone in mind who's a guy, i.e., male. I believe you, though. This might be something that differs regionally.
"Silicon person", "silicon gal" etc would be weirder phrasing. "Silicon specialist" maybe but I don't personally think any of this merits discussion.