Noetic isn't something you can understand by reading a dictionary definition, though I understand why you tried. (And I'm also a little surprised you found it at all where you did.)
It's actually a rather deep concept. I'm still struggling with the details myself, and probably always will. It gets tied up in discussions of the mind, the heart - the nous - I should also say it is the way by which we can know God.
That last bit is probably the most important for the discussion.
Biologists don't go looking for a nous though ...
I'm not going to speculate on how the Church might view Neanderthals specifically. But if they could know God, they were human persons.