This is indeed a Snowy Egret. What looks like backwards knees on a bird are actually their ankles. Think about the last time that you ate chicken. The drumstick is actually their calf muscles. The thigh bone is inside the body and immobile. What looks like their hip, where the leg connects to the body, is actually their knee.

That immobile thigh is very important to the bird, as it serves as an attachment to support the lungs and air sac that give the bird enough oxygen during flight. Birds are the only land animals that have immobile thigh bones.