The call history with drug traffickers was from months before his arrest on "drug consumption", where while in remand the police "made the connection" to the previous crime. He denied any involvement, but a court ruled that he owned the phone number. So....
Source: https://www.vice.com/en/article/88xn7b/death-penalty-singapo...
What if he dialed the wrong number?
What if it wasn't actually his phone, but was a shared phone among friends or family members (not uncommon in people without stacks of money)?
What if he lost his phone or it was stolen?
What if someone else had the number before him?