I like your thinking and reasoning. My canon Shepard is engineer and I have some similar backstory for her. Granted, she was a colonist and not as smart as yours, but she was pretty savvy with tech from young age, what with helping her father and brothers around the homestead.
And good reasoning about the smarts. It does seem like tech based classes are more intellectually angled than combat/biotic ones.
Thanks. To be honest, she (my engineer) has the most in-depth backstory and history out of any of my Shepards. Most of them I'm fine with thinking of them as fairly normal with fairly normal upbringings that aren't really that interesting, but my engineer is one of the only ones that I really put thought into her upbringing and truly made up a story about. Shall I tell you why she became good with omni tools? There's a story behind that too, though it is a rather simple and... Childish reason.
As a child, the first time she saw an omni-tool amazed her. It was just so cool looking to her, the way it glowed and the hand part kept spinning and spinning. It awoke a love for omni-tools that she didn't know was there until she saw one. Kind of a simple reason, but seeing one left a very strong impression on her, and things stick with you a lot more when you're a kid. Sometimes small things like that can start a lifelong passion. And once she finally got one, she made sure to learn everything about it. She's the kind of girl that will literally fangirl squee (okay not literally, but you get the idea) at the sight of a new model of omni-tool, even if it's worse than her own custom one.