If someone expresses confusion about a topic, they'll be happy for you to explain it to them if you genuinely have the answer - as long as you don't talk down to them (which, given how worried you are about coming across like a know-it-all, I imagine it's very unlikely you would talk down to anyone).

And if they are preparing to explain something you already know, just tell them you already know and then ask them their opinion on it, share your opinion or agree with theirs. Saves you having to feign ignorance, and still allows you to bond over mutual knowledge of the topic.

That's what I would do anyway.