They are in the same family. Black-eyed peas and Purple hull peas (Vigna unguiculata) are a variety of the cowpea and are part of the family of beans & peas (Leguminosae or Fabaceae in the USA). Although called a pea, it is actually a bean.
I've got a 24x12 purple hull pea patch and the plants are just starting to form pods. I'm looking forward to the first batch of peas. Pork steaks might be on the plate as well. Yours look very good.
Our family loves field peas and cow peas. Cow peas are great for small gardens and are prolific producers around here. We have plenty of them out of this summer's garden efforts...now I need to round up some pork steaks!