giant zucchini oddity

Upon returning from a week's vacation recently we were greeted by an enormous zucchini, four inches in diameter and perhaps 15 inches in length. That wasn't a surprise; everyone has seen and fled from much larger.

Two things did get my attention. First, when we left all the squash on this vine were a few inches in length. The others grew slowly, while this one went all Attack of the 50 Foot Woman on us. Second, it was of excellent quality! Unlike other bloated zucchini monsters with their spongy flesh and unpleasant seeds, this one was firm, mild, and had seeds no more developed than you'd typically find in one a fifth the size. Huh?

Age must be as significant a factor as size in the quality of the squash. I wonder what causes one to go berserk while the others bide their time? I've seen the same with cucumbers.