Park closing is the time that no more guests may get in line to go on a ride. Those already in line will be accommodated.
(For general guest park closing followed by a party, as of the general closing time you need a wristband or other ID to get in line.)
Fireworks scheduled immediately after closing are for all guests in the park unless otherwise advertised like for a party.
If you are in a restaurant at closing then you are not expected to hustle out although in some cases you will be escorted to the park exit when you are done.