Why was Captain Léon changing spoon positions of Jane Clayton's plate after she left?

My opinion (as opposed to fact): Leon is practicing his deep affectation of good breeding. He fancies himself equal to all who can show they have the best backgrounds -- including the nobility. He corrects Lady Jane's silverware position when she storms out of the dinner because that is how you place them when you are finished. This would signal a servant to proceed with the next course or clear the table.

It was made clear in the movie that Leon is from a peasant background. I think it goes as given that he is driven by huge ambition.

I don't remember the exact dialog, but I do recall that he stated or implied that his ultimate goal is to have the same status as an aristocrat. Some of the quickly achievable goals to do this is to study and practice meticulous fashion taste and etiquette: notice in the picture the way he is dressed and the way the dinner table is set. But the much more difficult things to achieve are: wealth, reputation, and status. He plans on getting the first two by stealing, killing, and making up a credible cover story of danger, and his "noble" self enduring it all. The status he plans to get when other doors open to him because of the favors he will receive when he garners political victories in Africa.