A number of ice plants (Aizoaceae) apparently have the common name pigface, including common and invasive Carpobrotus and Mesembryanthemum species. Ruschia is in this family. I'm not sure if the word is regularly used in all English speaking countries, but it is used in Australia, where some of these plants are native. As far as I can tell, the name is very general--similar to the word vygie, which can refer to any member of the family in South Africa.
Presumably one of the many plants in the group reminded someone of a snout, and I can imagine that might be possible given the variety of forms in the group, but I see no connection whatsoever between the common name and the form on the plants that I know.
