There are so many variables to low adhesion that it’s very difficult to speculate what the cause was without testing the railhead on the night. Even then, if it was anything like my neck of the woods that day, the torrential rain could have washed off or diluted any evidence of low adhesion.
Is it possible? I’d say yes, I don’t know the chemical makeup of fireworks but any small debris can make the railhead slippery. We have a wood factory near Chirk that can cause issues apparently (like the flour mill example above, I’ve never encountered issues). But I’ve had some scary moments where a level crossing is at a station and the wheels pick up because of the fumes from the exhaust, that’s in good weather too. Low adhesion can come out of nowhere and will catch out even the most experienced of us.
It CAN be worse than some people imagine too. Last year, I travelled nearly a full signal section in emergency and only went from 35mph down to 30mph. Luckily a tunnel came to my aid and I got some grip back on the approach to the red. This was in a 75mph—>50mph section too so the signals weren’t close.