I should not have to worry about not being able to show any of that. If the people interviewing me don't understand what I did without me showing them, then I am certainly applying at the wrong company.
Don't underestimate the value of some general understanding / intuition of how systems will probably work combined with a little googling.
On a side note I also worked with RFID readers, they were yesteryear's Internet of Things :).
It's probably more common for recent graduates to have public repositories than for the majority of senior devs. Then again I'm sure there are other pressures graduates have to deal with that senior devs don't.
From my recent experience (and anecdotal evidence) it seemed it was becoming a deal breaker for companies but maybe I reached that conclusion too quickly.
It'd be nice if tech recruiters actually had a background in tech.
On the occasion that they do (super efficient manufacturing plant), the same rules would apply.
TLDR; The carpenter analogy is horrible.
It was strange, but that happens there.