it doesn't really make sense to say that "I understand reductionism".

How much do you really understand if you say something about the topic that you believe not to make sense?

I'm remembering having a good understanding of it back in middle school (although a) I know that memory isn't always trustworthy, and b) I definitely didn't know the lingo).

Not having updated one's beliefs on a topic since middle school doesn't suggest deep understanding.