That's a cynical way to put it, if technically correct. Manipulation has a negative connotation for people, but people don't communicate for exclusively malicious reasons.
You might as well say that any conscious entity only acts out of reason, to get food, joy, rest... Or that it isn't possible to speak without words. That much goes without saying. Everyone knows that, which makes this an odd thing to bring up in this thread.
And I'd suggest that you can't prove that a conscious entity without reason ceases to act. We've all surely done something or other for "no particular reason" even if an outward observer might assign one.
Does that mean it's possible to speak without meaning anything in particular? I genuinely don't know.
But I can be sure of one thing, that speaking with the intent to achieve one thing, almost never achieves that exact thing. Is failed manipulation still manipulation? Is unintended manipulation still manipulation? People interpret meaning where non was meant all the time.