Drugs addict, i believe this 2 bandits need money for drugs.They never think about 10 years in prison for their crime, they only think how to get money fast and easy.
Drug addicts desperate for money normally don't show this type of sophistication. In this case, these two goons worked out a well-planned operation, and managed to convince the victim to do trade with them. They also selected their victim wisely. They chose someone who is inexperienced, and less likely to report the crime to the cops. Also, they knew that it is difficult to prove the theft of Btcoins.
you are right , this is a planned out operation, these goons have looted from a guy as they were desperate for some cash to fuel their drug habits, however he could have been more secure by leaving no traces that he has bitcoins, even here there have been lot of phishing attempts on users who were alleged to have huge amount of bitcoins, so one thing be safe and keep your mouth shut about your own bitcoins.