Answer by Rory Young:
Okay, my answer is purely my own opinion and not backed up by any behavioural study or the like.
Leopards are solitary animals and as such are used to dealing with situations on their own. Lions are gregarious animals used to being supported by others. Therefore a leopard if attacking a group of people out of a defense mechanism will attempt to do the job entirely on its own. A lion on the other hand is more likely to rely on support from the other members of its pride.