Welcome to BYC. Glad you decided to join our flock. I'm a chicken person and don't know much about ducks (although I've had a few), but I would suggest posting on our Duck section in Other Backyard Poultry under the Forum section at the top of the page and taking advantage of our Duck experts there. Please feel free to ask any questions you may have. We are here to help in any way we can. Good luck reconnecting with your duck.
Glad you could join the flock! I'm afraid I'm not a duck person but I'm sure the duck experts will be able to help you. I would suggest spending some quiet time with your duck so he can used to you again. Sitting and talking to him should help his become reacquainted.
You could sit out there with him (if weather permits) and maybe listen to soothing music. I think his curiosity might get the better of him. Maybe he thought you abandoned him and is punishing you for it. If he is your only duck, I would imagine he would prefer company. OR maybe his little duck brain doesn't recognize you.
I had a dog like that. We boarded him over a weekend while we had a short trip. When we went to pick him up he growled at us. We had him for several years and that's how he greeted us.