A pork pie (as seen above) normally has a fairly solid meaty filling surrounded by a jelly to fill up the case. The pastry should be hot water crust, definitely not flaky. These pies are finger food and normally eaten cold as a snack or as part of a picnic lunch. This is generally what is meant when a pork pie is referred to. The stuff about people hiding the wrappers is partly because they aren't very good for you, generally being quite fatty, so you might want to hide the evidence that you have eaten one form your other half!
Meanwhile other pies have gravy and sometimes vegetables in them. The meat might be pork, chicken or beef (occasionally venison). This type of pie would be eaten hot with potatoes and veg on the side, usually with a knife and fork, as part of a main meal.
A ploughman's doesn't normally have pie. Traditionally it is simply a piece of chunky buttered bread with cheese (normally cheddar or stilton), perhaps accompanied by a chutney.