sweet potato harvest

I harvested my sweet potatoes today. I just had on small row that I grew at my community garden. With a very bad vole population this year, I was afraid I find all sorts of half eaten tubers. But only one had nibble marks. And many of the tubers were pretty good size. I was surprised to see several were sprouting already - underground. What's that about? The hot weather? I'm glad I got them out of the ground a bit early. I normally would wait 'til after a frost but I thought I'd get it done now.