Since you are talking about a transcriber, I'm guessing this was transcribed from a performance, maybe? In any case I imagine it was played fairly freely
I got it from here at 57 seconds. Whenever I stumble upon a strange guitar, drum, or piano rhythm I want to understand it
In the bar you are talking about I hear no difference between the 32nd notes and the septuplet 16ths. I would guess the transcriber was trying to find a way to make the math of the notation add up correctly so that you have 30 notes over 4 beats. Back in the good old days they (e.g. Bach) would have just written 30 32nd notes and left it to you to figure how to space them over 4 beats. Chopin would have put a brace over the 30 32nd notes with a "30" label.