Depends on what you mean by registered. If you own 50 guns and bought them new from a gun dealer in the last few years, then yeah, they are "registered" in a sense. If your 50 guns have been collected ... legally... over the last 50 or 60 years, then many, and perhaps most, will not be "registered"...but of course you know that. My first gun, a .22 rifle, was manufactured prior to WWII. My Dad bought it from the guy that bought it new...he paid $5 in about 1942. It does not even have a serial number.
I read what the man said as meaning that guns taken from criminals were not registered to them for various reasons...probably because many of them were felons and could not guy a gun legally, and so procured them by theft or buying them on the street, and others, because they intended to use them illegally, were not dumb enough to us a gun that could be traced back to them. The point being that only law abiding folks buy their guns through legal means, and if registration is designed to connect the registration back to a criminal, then registration as a concept is a failure. But you know that too.