What caused leakage in my cheesecake?
Spring forms are not entirely liquid-proof, so anything liquid can leak out of the form while baking. I personally set off the fire alarm a month ago trying to make potatoes au gratin in a spring form. In my experience, what tends to leak from a cheesecake is fat from the crust. Many recipes recommend baking a cheesecake in a water bath, which both helps the cake bake evenly and neatly prevents anything from leaking onto the bottom of the oven.
I will say that using beaten egg whites for an oven baked cheesecake is somewhat unusual. Most recipes include whole eggs, and you would try to avoid beating any air into the batter to prevent cracks from forming.