The difference is subtle. If it was important, the speaker would add more details. The difference in verb tense alone doesn't convey a lot of meaning.
"Close" means the speaker is thinking of the action as a single unitary event at a single point in time. Tessa didn't pay attention to any details. The door was open. She heard something. She said to herself "The door is closed."
It takes several seconds to close a door, and if you pay attention you may notice a series of different sounds. There might be a slight whoosh of air. There might be a squeak from the hinge. There might be a "click" as the bolt hits the plate, and then a "snap" as the bolt slides into place. There might be more sounds Paul locks the door after leaving. If the speaker is thinking of the action as extended in time, they might say "closing."
For example, "Tessa heard Paul closING the door, but before it was closED he stopped. He stuck his head back in and called 'I'm going to the supermarket, do you need anything?'"
On a subway, you might hear an annoucement, "Please step back, the doors are closing." It wouldn't make sense to say "Please step back, the doors are closed." If the doors are already closed, you don't need to step back.