Red maple (Acer rubrum) "flowers are structurally perfect. The species is polygamo-dioecious. Thus, some trees are entirely male, producing no seeds; some are entirely female; and some are monoecious, bearing both male and female flowers" (1).
From your question, it is obvious that you either received a female tree or a monecious tree because your tree is producing samaras.
Source: (1) http://www.na.fs.fed.us/pubs/silvics_manual/volume_2/acer/rubrum.htm