Shapefile specification does not have a geometry type
Multipolygon. The closest one is
Polygon (with Z or M added). However, the USA is a multi-part polygon indeed meaning that it is represented as a single row in the shapefile yet the geometry itself consists of a few parts.
arcpy code run on shapefile:
> c = [f for f in arcpy.da.SearchCursor("countries", "SHAPE@")]
However, if you import the shapefile into some other more sophisticated storage format, such as PostGIS, the polygons would be stored using
Multipolygon geometry type:
Importing with configuration: ne_50m_admin_0_countries, public, geom,
mode=c, dump=1, simple=0, geography=0, index=1, shape=1, srid=4326
Shapefile type: Polygon PostGIS type: MULTIPOLYGON Shapefile import
SQL in PostGIS:
select ST_AsText(Geom) from ne_50m_admin_0_countries
where sov_a3 = 'US1' and type = 'Country'