It made no difference to Christian whether or not this old man in this store had set up the situation that led to his brother's death.
And in a way, if that were indeed the case here, then this young man would even feel a little grateful to the owner of this store!
But don't get it wrong, it's not that this young man hated his little brother or had big problems. He hadn't. The two of them had always gotten along very well until Tristram had met Misty.
At that time, Christian had already fallen in love with Misty, even before that young man killed by Minos married this girl, and Christian wanted to have her at any cost...
This young man had always had a stubborn personality, and when something entered his mind, he could not stop thinking or acting to make it happen.
Misty messed with Christian's mind in such a way that the formerly womanizing and wanton young man had quickly lost interest in other women.