I would say you have made a mistake by not giving your friend the proper knowledge about investment in bitcoin, but at the same time you have done a good job. Don't get discourage by this. Rather learn about it and share your knowledge in the future. Don't tell people what to do with their money. Show them the road and if they understand it, they will walk on that road on their own.
What you did is already done. So it's time to teach your friend more so that he will not make any mistake and blame it on to you. And I am sure when your friend comes to the forum, there will be many ready to teach him more. And one thing to keep his assets safe, teach him about private wallets.