I have an uncountable number of assumptions to get by in the world. I have this vast heritage of knowledge. I try to keep a handle on why I believe what I believe, but it's not easy, and I'm sure I slip up. An alien would share none of these.
Take counting. That's super important for lots of stuff I do every day, like, what day it is. the https://en.wikipedia.org/wiki/Munduruku people don't count. I'm sure we could work something out - but we all gotta sleep and eat and stuff so we can sorta work out a framework for understanding wants and needs and such.
An alien doesn't require wants or needs. they may do stuff that we label wants and needs, and it might be a good mapping, but who fucking knows? Aliens are alien.
The water is triangular sentence is a great one. do the aliens mean they know that oxygen and 2 hydrogens don't make a straight line? And they know we mean oxygen and two hydrogens are water? and they know 3 non parallel lines in a plane means triangle? Maybe? Sure? maybe they mean all Ferrari's will be consumed for fuel.
Mean, dear reader, doesn't even mean anything, because they're aliens. I mean, you can point at math, prime numbers are a great one! but like, do you need prime numbers? Who knows? That's the path we took, but what would an alien need? I don't know. You, dear reader, may have strong opinions, but I'm pretty sure you can offer no proof.