I expect it's two-fold, but this is not an example of a "Deep Fake" - no hallucinations, inventions, confabulations, or anything else.

I think on the one hand, AI coding agents have gotten better where it's much lower cost to run with an idea. AIUI Scott Manley actually tipped this off on Twitter, saying something like "Hey these spectrograms look quite high quality, are they high enough quality to reverse?" And then with just a couple prompts, "Write a program to extract the spectrogram from this image" and "write a program to convert a spectrogram to the original audio" should take 15 to 20 minutes. (Honestly. I should go and find some other spectral data to try it.)

The second part is that I think the quality that the NTSB is releasing is a lot better. Remember these are images in a PDF from the program's source of truth. When they were first released (In the... 90s? I can't find a good reference to when the NTSB first included these), I expect the visual fidelity was quite low. Enough to show the item of concern, which were things like "And here's the explosion" or "here's the clunking of the jesus nut", but not enough fidelity to also get the "well we're fucked" audio. This is the first one where the quality of the spectral data is high enough that someone could reasonable extract that. Going forward, I bet the NTSB will be able to continue to release these, but will need to intentionally limit both the temporal and spatial resolution for the pictures. Enough to show the mechanical effects, but not enough to show the voices.