My hot take on why every time something chemical explodes people say "IT'S GOTTA BE A NUKE" is that a) most people do really believe that mushroom-like clouds are unique to nukes (they aren't), b) most people (in the West) don't have any sense of scale for explosions.

I mean, just to give you a sense of the latter, here's the Trinity bomb's first 16 seconds, with the Empire State Building for scale.

And the mushroom clouds from these first nuclear weapons were HUGE, by human standards. Like, "hard to actually imagine" huge. As I like to tell everyone who looks at the NYC skyline with me, the Hiroshima cloud rose to 11X the height of the new WTC building over 15 minutes.

Now we can get into discussions about micro-nukes, but the fact that people don't even realize that's what they're talking about is my main point here: these large conventional explosions are still TINY compared to nukes that are considered "small" today, like the WWII nukes.

(My "in the West" caveat is only because there ARE people who are familiar with relative explosion sizes, but that's because they're living in parts of the world where there are a lot more explosions more regularly. It's not a bad thing to not be used to explosions...!)