Like sibling comment elucidates, code-golfing is just using tricks to get the size of a program down without impacting its functionality. This could be as simple as using single-character variable names or something more complicated like including a decompressor that expands some packed code before execution.

If you got the decryption code plus the payload small enough you could theoretically put the whole thing into a data URL (a URL that doesn't link to a remote resource, but contains all the data needed to display a web page). This data url could theoretically then be encoded into QR and accessed entirely locally on anyone's smart device.