The first stage of grief is often denial. He can’t quite believe it happened. He isn’t ready to talk about it. To talk about it gives it more reality. So he distances himself from the tragedy by chatting about unimportant things and keeping himself busy by asking you to take another friend on a tour. My guess is that it hasn’t entirely hit him yet that his friend is gone.
As his friend, the best thing you can do is tell him how sorry you are to hear of his friend’s death and then to let him know you are willing to listen if at any time he wants to talk about it. Don’t pressure him but do check in every now and then to see how he is doing. People grieve in different ways and in their own time. If you keep the lines of communication open, he may eventually want to share. If, however, he is a very private person, he may choose to share his grief with only a few. Be accepting and kind. Grief has no “normal.” We all do it in our own way.
I wish you well.