Why don't I have to pay capital gains on the sale of my house?

I sold my house after living in it only 18 months (less than the 2 year threshold), so I expected to have to pay capital gains tax on the profit. However, after I input all my info into TurboTax, I got this message: "You don't have to pay any income tax on this sale of your home because your gain of $10,702 was less than the maximum allowed of $375,000." Can someone explain why I don't have to pay capital gains even though I lived in the house for less than 2 years?