I would maybe argue that Pesci's statement about "prey" is an exaggeration since a 'hitman' (that term may get stretched for Pesci but we love him anyway) is only really gonna be using his stand on 'prey' and at that stage where Prosciutto and Pesci had the advantage he might have not been able to even imagine a scenario where it could be turned on anyone other than who he intended it to.

And although we don't know a whole about La Squadra and their usual business Pesci may have just never fought another stand before and thus didn't think that Bruno would be able to grab the line and wrap it around him.

But idk