You are wrong. Thank you for playing our game.
The summary above from
mass.gov is actually not a correct summary of the law.
MGL 140 131C is the law on transport. It actually says only handguns can be loaded and must be under your direct control. Everything else, unloaded. Large capacity long guns in a locked container or trunk. The law is SILENT on unloaded handguns and unloaded non-large capacity long guns. Go read it again...
So sure, a cable lock on your handgun is "enough" because it is more than is required. You can legally throw unloaded handguns around your car like skittles. Now when you park you had better meet storage so that cable lock helps...
But of course this is not mass prudent. 99.99% of police think your handguns need to be in a locked container and will act accordingly.