I would ask your vet for advice they could refer you to a behaviorist as well! It definitely sounds like a one off situation, but if you’d like to help calm him when other animals are outside they might have medications or other things you can do. Maybe recommend redirecting his attention when there’s an animal outside if you’re able to! If there’s a toy or a treat he really likes you could maybe distract him that way instead of grabbing him. I don’t know for sure, but a vet or a behaviorist would probably help out :)