Who needs to understand them? The algorithm? What does that even mean? And if you mean the authors need to understand how the algorithm works: Wrong again. They probably do, but even if they wouldn't their algorithm might still classify correctly.
Science works by separating out the disciplines. Frankly I think "defense against the terminator scenario" could and should be a scientific field on its own at this point on the level of solutions to global warming.
This is interpreted as a side effect for now. That is, until you tell the computer to do something based on the topics.
If the output of AGI demonstrates intelligence in finding a solution, whether it had "understanding" or not doesn't matter. The only thing that matters is its power to turn inputs into outputs.
The Turing test crystallizes this WRT human language interaction. Assessment of the intelligence of a machine doesn't depend on understanding, consciousness or any of the other baggage dragged in.