I think the problem here (and the reason the OP feels it "tastes artificial") is too much coincidence:
First, we have deer in the forest, but for some unexplained reason the dragon cannot find a single one, so he steals a sheep, and is so unlucky or careless doing it that he is seen by a shepherd. The fact that the deer are there and he can't find any seems too unlucky, piled on top of the bad luck of a witness.
Then the deer come back, and he doesn't have to steal sheep anymore? What caused them to disappear so long he grew hungry, then magically return?
Then livestock start disappearing? What is causing that? That is more extremely bad luck.
Then a child (too conveniently) goes missing? Why? That is more extremely bad luck.
If you are going to start a story with bad luck, make it one bad luck incident.
1) The Normal World: You have a dragon in a forest. He hunts deer. This is his normal world, he is happy and content, there are plenty of deer, he is in balance as the top predator in his environment. If you wish to make him smart and sympathetic, he takes deer intelligently: He only takes the old, ill and lame, he doesn't take fawns (as a lion or wolf would) and he doesn't take their mothers, or pregnant females, or young females. He culls his herd, killing quickly to minimize suffering.
2) The Inciting Incident: Humans hunt deer, too. They always have. A group of bowhunters happen to see your dragon take a deer, as it does every day, or once a week, or whatever. If they don't know what a dragon is, they start firing at the monster poaching their deer. Our dragon fights back in self-defense, the arrows hurt and could kill it. In fighting back he kills two of the hunters, and the rest scatter and flee.
3) The Escalation: The dragon doesn't understand the humans, and has to treat himself and heal his wounds. The humans return to their village, but now they have a monster that has killed two men, and it must be exterminated. It is too dangerous to let live! If you still want the kid involved, they bring it up: It flies, they saw it lift a deer! Surely it can snatch kids from the ground, or sheep. They create a posse to hunt it, and this dynamic drives our dragon out of his normal world. The dragon is not surprised by them, but terrified, still injured, and aims to escape. (I presume from your other questions he ends up captured, that is fine, the villagers intend to sell him or something.)
Thus ends Act I.
The only bad luck is the dragon was unlucky enough to be seen killing a deer. Human hunters naturally wander, follow spoor, and deers naturally forage and wander randomly in search of edible foliage. If you want to make this slightly more plausible, set it at the beginning of winter: The deer have to wander more to find food, the hunters want food to store for the winter so they are more persistent and work farther into the wood, and the dragon has to fatten himself up for winter as well, so he is eating and hunting more often.