Your egg whites were cooked by the alcohol in the extract. Cooked, in this case, means denaturing, which means unfolding the protein molecules. There are many ways to denature proteins. Acid, such as vinegar, will denature egg proteins, which is why some people suggest adding vinegar to the water to poach an egg (a practice I disagree with, but that's another subject).

Ceviche, as another example, is fish which is cooked (denatured) in acid (such as lime juice). Although heat is not used, the fish is still cooked. (Note: the acid will kill some bacteria but is not as effective as cooking with heat, so be sure to use fresh fish from a source you trust.)

This is similar to how burning means combining with oxygen, so you can burn metal (rust) without heat (most easily by adding water).