He sounds like he wouldn't do it on principle, but I don't understand the technical reason why he couldn't.
And even if he was willing to have his blog redirect to that other site, there's still the issue about all these other misprinted codes. If they point to $randomblog it's mostly funny. If they point (via the redirect) to $possible_competitor, it's much worse
There is no technical barrier to redirection. What he actually says is "What does that mean? I’m guessing they think I can somehow magically cause that QR Code (which they accidentally used in something printed?) to redirect to another URL. I don’t think they understand that the QR Code IS the URL."
Notice the word order. He's "guessing what they think", and his guess is that they think he can "magically cause the QR code to redirect to another URL" -- the object of the sentence is not his domain, and not his URL, but the QR code. (He's saying that they've phrased it as if there is a QR code database where the code must be looked up.)