Yeah, I don't believe this at all. If Chris had done ANY of this, he would have bitched to Facebook about how some neighborhood dog had dented his car or had gotten him in trouble. And trust me, if a 13 year old had seen his junk and had told people about it, he'd definitely been posting shit on Facebook about the trouble he was in because people don't understand him as a tom girl.
I kinda doubt this. Even as stupid as Chris is, he does realize that killing a dog might cause him bad consequences. Doubly so because he's paranoid, spineless and believes in a centralized, vast, powerful troll conspiracy that has IRL agents, and on multiple occasions have interfered in his life with very serious consequences.
(Snyder, Megan, the poster campaign... I wouldn't be surprised if he thinks a troll agent slipped into the house, and wired the Kreurig to commit harakiri.)
He also knows that there is good and evil in the world, and most definitely considers himself as a fundamentally good and decent person. (as opposed to those darn, pestering evil trolls!).
Posting about killing a dog in a careless way would tarnish his good image and reputation, so he'd never do that. (Unless it had somehow already gotten out.)
Chris's very vague religious beliefs also seem to center about a divine entity that rewards good people such as himself, and punishes evil people like trolls.
It also seems to be an ingrained belief in him, that being good naturally and immediately carries an earthly reward* and makes people act nice towards him.
(Remember how at first he tried to convince the trolls that he was a good person, so they'd seize targeting him?)
Now I'm not saying that it would cause Chris immense stress and grief to have killed a dog by accident. But he sure as hell wouldn't own up to it, unless pressured or more or less forced to.
* I believe that it's especially this factor that has caused Chris huge frustrations over the years, and seen him sink into untreated depression. He knows he is supposed to be rewarded in a generous and timely manner for "good" acts, and for being a good person, yet it rarely seems to happen. He knows how the world is supposed to work: He's a good, kind and righteous person, and therefore should be rewarded with plenty of vidya, LEGOs and china. Mhmmmnjaehm-mmmore of that-eh- sweet, precious precious china than you can shake a stick at! But somehow the system is broken (most likely due to those darn, pesky trolls!) and despite being good and kind, he gets neither china nor material rewards. It's just not fair and doesn't make sense!