To be honest, I've read the first and second books and not entirely sure what you mean.

There's a scene at the end of the second book where the aliens offer to build a neutrino communication device for humans but the humans opt for one that uses gravity waves instead. It's a very brief reference, I don't know why the parent would have brought it up.

Yeah, I was misremembering; I thought they actually did end up using high energy neutrinos.

I am finishing up the third one and also have no idea.

Many people have thought about neutrino comms