It is common to use nouns as modifiers of other nouns. The term ice cream serves that adjectival purpose, modifying cone.
The waffle cones and sugar cones that are traditionally used (at least in the US) to hold ice cream were designed for that purpose. While the cones could be, and are, used to hold other things (and may even be eaten plain, if one is so inclined), their most common usage serves to define them, regardless of how they are otherwise used.
When they hold frozen yogurt, they still are ice cream cones. Filled with jelly beans, likewise. But note that the cones are often referred to without the ice cream qualifier. They may be called sugar cones, waffle cones, cake cones or simply cones, as in the ice cream vendor's query, Cup or cone?
Many other noun/noun terms keep their primary designation even when the item is put to purposes other than those described in the modifier. A car park is still a car park even when there are no cars on it and it is being used to host a fair.
The dividing line is between a noun being used as a casual modifier and a noun/noun phrase becoming an established term is not bright. By definition, the primary noun has other uses or no noun modifier would be needed. But when a relatively fixed relationship has been established such that the modified noun now has a distinct and relatively stable meaning, the modified name sticks, even if the item is put to another purpose. A tea bag applied as a poultice is still a tea bag.