It is a very different kind of life form though so many things that applies to other complex being doesn't apply to them. Being a large single cell means that they learn by changing its proteins and other internals, very hard for us humans to reason about and understand since it is so alien compared to just having nerve cells with physical connections.
So your statement just seems to be your bias thinking that a slime mold couldn't possible do any reasoning. Cells are much smarter than most thinks.
Edit: Anyway, apparently slime molds can communicate what they learn by sharing those proteins. So they do have a language, it is like a primitive version of how human bodies cells communicate. So your point still stands, reasoning seems to go hand in hand with communication. If you can reason then it is worth it to share those conclusions with your friends and family.
They also taught slime molds to cross a bridge for food, and it learned to do it. Then they got the slime mold to tell other slime molds and now those also knew how to cross the bridge. It is pretty cool that slime molds can be that smart.
https://asknature.org/strategy/brainless-slime-molds-both-le...