The idiom means that there is usually truth behind a rumor, but the context is saying that the generally accepted reaction was that there was no truth behind the rumor of his sacking.
Context: People usually make things up out of thin air without any proof was the generally accepted reaction to his sacking.
Hypothesis: no smoke without fire was the generally accepted reaction to his sacking.

Given this context, determine if the hypothesis is true (Yes, no, or unknown)?