I don't think it's any technology, and he doesn't specifically say so in the episode:
But you mustn't think of us as omnipotent. No matter, what the Continuum would like you to believe. You and your ship seem incredibly powerful to life-forms without your technical expertise. It's no different with us. We may appear omnipotent to you, but believe me, we're not.
The use of technology in the analogy may just be coincidence, and the Q's incredible power makes them seem omnipotent, but they aren't omnipotent have their weaknesses all the same.
The Q to me are like humanity in Isaac Asimov's story The Last Question
. The Q probably have a history similar to humanity, but grow beyond that to become demigods. Whatever weaknesses the Q have, they surely are irrelevant to us anyway, as such a weakness would be on par with the destruction of the Universe or something like that.
I have to agree.
It seems that the whole point was that, even though the Q may have weaknesses, they are so far ahead of us, that those weaknesses might as well be impenetrable barriers for human beings.
Kind of like Federation Starships having the "weakness" of torpedoes being able to pass thru the shield frequency if you have it. That don't matter a damn if all you have is bows and arrows to shoot at it.