Having taught in both inner city, predominantly black schools and rural, predominantly white schools I will cop to being paranoid about racism. I see the looks, and hear the comments when people hear where I have taught. I am well aware that many racists know that they can't explicitly verbalize their racist thoughts and so couch them in a slightly twisted way and give a nudge and a nod and a "you know what I mean." So I will cop to be a bit sensitive to matters of race (maybe even a bit paranoid). That said, I am consistently surprised by how naive and sheltered most of the Slashdot membership is about racism. Or maybe they will also tell me that the Confederate flag isn't a symbol or racism. I enjoy that one every damn school year. As for assuming the grandparent was racist, how the hell is that racist? It has nothing to do with the race of the grandparent, it has everything to do with what they said and how they said it.
And it is possible that I am missing a level of sarcasm and satire with the grandparent. Maybe they are actually advocating for gun locks with biometric recognition. That said, my experience with people who say "you know who I mean" has been universally negative. In an actual conversation I frequently need to wait for less than five minutes before you hear about how "those people don't know their place anymore."