There are multiple effects caused by fire that have an effect on electromagnetic signal propagation. Someone wrote a PhD thesis on this:
https://researchonline.jcu.edu.au/2028/2/02whole.pdf
The gist: Particulate matter attenuates signal (present in smoke), but the larger effects are from the signal refraction due to the thermal bubble created by large fires, as well as the electrically charged particles causing large fluctuations in the electron density of the atmosphere - the same effect that occurs when large solar storms hit the earth, although with these the electron density in the near space region (above the atmosphere) is affected.
So yes, this is perfectly conceivable and real!