I have mentioned this to the dev team before that they need to look at the structure of animations(clip) in Unity. Animations or clips have properties and further they belong to a component controlling them like animator or animation component. This controller also has properties. So you can tell each animation to loop or not, not the controller.
Currently on sketchfab such properties are only on the controller. Loop means loop the list of animations. There is no individual animation control. Also you cant change the list (add remove clips ) you will have to construct your own list for that. calllng getAnimations will just return a list of all available animations.