Mandarin sprout with heart shaped leaves?

I’m basically a noob when it comes to growing plants, and I’ve just realized that mandarin leaves are not supposed to be heart shaped lol

I’m growing a mandarin (or what I thought was one) from a seed I got from an organic store bought mandarin. It has four leaves, three are heart shaped and the newest one is more like an oval. The plant itself is about an inch tall. Another plant couldn’t have gotten inside the pot because I’ve been growing this inside so far to avoid pests attacking it. Can anyone tell me what happened??