"Somewhere I heard that if an item was sent to you that you did not order, you have no obligation to return it or pay for it."

This occurs more typically when a charity or business sends a stamp or a $1 bill or a sample issue of a magazine or some small item, along with an invoice or request to give to the charity, subscribe to the magazine, etc.

In those cases, you can keep the item -- or toss it -- without obligation to respond / donate / subscribe / or return the item.

The few times I have received a mis-addressed item, I've always returned it to the post office.
But your practical recourse in this case is probably limited or nil unless it was a Signature Required delivery.