I just happened to think of something.
I have used the technique many times, and noticed that if the saran wrap lays on the marblizer very long, it starts to wrinkle a little. That would cause the paint to accumulate under the wrap in little ridges... which when pulled might produce those "worms".
Again, I think spraying it heavy is part of what produced the pattern.
I think some test panel work might just reveal the key to the mystery.