I've had that happen to a package of mine as well and it turns out that the visible damage was just the package being damaged and not the actual part I ordered.
I had ordered an oil pump for my truck before and I was worried that the oil pump had become damaged during shipment.
So I went to pick it up at the post office and then luckily it was just the package being damaged and not the actual part or item that was being shipped.
So it can sometimes mean that the package is just damaged and then it can sometimes mean the item has damage to it that the postal employees can see after the package has been torn or damaged.
I wouldn't worry too much though as it's likely just the package being damaged and nothing else although there is the possibility of the item being damaged as well.
If the item is damaged then you should contact the seller and have them sort the situation out with the USPS who should then cover the cost of the damaged item through insurance.