Surprisingly the victim hold his Bitcoin worth of IDR 5.8M in centralized exchanges (Binance) and not using a non custodial wallet. Well it will depends on the victim privacy, did he clicked random sites? Publishing/tell anyone about his coins? did he using public WIFI to access Binance? did Binance information breached? we all don't know about it.
IMO the solution you should have separate cellphones, the regularly you use and the one used to hold Bitcoin (air gapped wallet). Gave him some portions of your Bitcoins on your regular cellphones, while you still hold most of your coins on the other cellphone.
IDR 5.8M is about 11 BTC at the current rate, it may look big, maybe the victim has activities as a trader who needs funds always available on the exchange.
The victim did not do what you mentioned, he had a robbery and one of the robbers was a former employee who was very likely to find out that the victim owned BTC and threatened to need the victim's wife so as to provide the password from his account. Luckily the perpetrator has been caught just not explained whether BTC can return to the victim.
IMO the solution you should have separate cellphones, the regularly you use and the one used to hold Bitcoin (air gapped wallet). Gave him some portions of your Bitcoins on your regular cellphones, while you still hold most of your coins on the other cellphone.
The point is always be careful with the device we use as a place to store crypto assets, Anything can happen but we can reduce the risk of loss by using tight security, although in this case account security is not the point.