Did you ever find out what it is? I have the same thing.
Hello,
These little red spots on arch of foot can be due to dermatitis skin, allergic contact dermatitis to the shoes or socks, granuloma annulare or stasis dermatitis. Stasis dermatitis affects the lower limbs mostly. It is mostly from vascular problems in the lower limbs. To confirm the diagnosis please get an examination done by a dermatologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.