you can try

Group group = themeDisplay.getLayout().getGroup();
long userId = 0;
if(group.isUser()){
   userId = group.getClassPK();
}

Hi ,

You can get it by using below method:
<%
User user2 = null;

if (group.isUser()) {
user2 = UserLocalServiceUtil.getUserById(group.getClassPK());
}

%>
user1:::<%= themeDisplay.getUser().getFullName()%>
user2::<%= user2.getFullName() %>

Here user2 will return you username of Richard Editor.

Regards,
Dhrutika