I only worked the last quarter of 2018 and made $9,150 income. And I got a refund of the amount that I was supposed to pay. ($1,213) What made me eligible for WITB?

I am a newcomer to Canada and worked as a self-employed individual. I am not really familiar with Canadian tax system and  it confused me why I got a refund and trying to understand if I did a mistake or if I should contact CRA.