[Answer]-Django pre_delete model method executing unexpectedly

Specify sender of signal in @receiver definition:

@receiver(pre_delete, sender=Item)
def copy_item_details(sender, instance, **kwargs):
    """
    :param sender:
    :param instance:
    :param kwargs:
    :return:
    """
    #Some code  

NOTE:
Signals should be placed in signals.py not in model.
According to Django docs:

“Strictly speaking, signal handling and registration code can live
anywhere you like, although it’s recommended to avoid the
application’s root module and its models module to minimize
side-effects of importing code.

In practice, signal handlers are usually defined in a signals
submodule of the application they relate to.”

Here is a link for you.