Wondering why my pound cake fell after I took it out of the oven

The main reason a pound cake falls is because of excess moisture. That could be due to extra moisture in your butter or flour to start with, or because it simply needed more baking time in the oven. I see the recipe does not direct you to test using a toothpick or other item to determine if the center is baked done. I've never found baking by the clock or by pressing on the top to be a good way to determine doneness, myself- and prefer using a straw or toothpick inserted in the center to assess the conditions of the inner cake a better method. A pound cake, or other cake for that matter, can look and even feel done, and yet have a deep pocket of ever so slightly underdone batter hiding in the center. And that will mean a fallen cake as it cools. Another reason might be that your oven temp is off, and baking too hot- so the outside is baked and set long before the center- and fooling you with the appearance and feel of a done cake. My bet is on the cake simply needed just a few more minutes in the oven. So next time, use a toothpick to test instead of the clock or pressing, and when that pick is clean- your cake is done and may well hold up better in the cooling.