I can't explain why he lied, I think just to get pity from the uke and get close to him.
As for why he left his family, that was clearly because they treat him like a bank, not a son. Even at the end his dad only stalked him just to try and guilt trip him into giving them money. His mother also isn't his bio mom, but his step mom from what's implied.
So he lived in a foreign country for 10yrs, working his ass off, no family, constantly supporting them with money and being the breadwinner, then returns and immediately gets yelled at for not wanting to give his stepmoms friend money/help. He's also 30, so he finally decided to leave his toxic family.
Though I don't get what the point of this plot was, when in the end we didn't even get any justice/closure about his family? Very weird ngl
I still did not understand why he lied or why he escaped from his family even with the official translation maybe I am just dumb