My first impression is that these are bites of some kind.

Does he have a dog? Flea bites on humans are often small, and don't always itch. Fleas will jump up from the floor, and perhaps bite only the foot area and ankles. If a dog sleeps in the bed, it may leave fleas also.

I'll continue to search... but in the meantime I'd put some Hydrocortisone cream on them, and see if they fade. If they do
then that is an inflammatory reaction.

Some people use too much soap in the wash, and socks may have a residue left after rinsing. When worn on the feet, the moisture from perspiration will dissolve the residue and leave little burns. Using a milder soap like Tide unscented in the white bottle, and doing a second rinse, may help.

The cluster of spots along the side of the foot resembles insect bites like fleas ...they will move along and bite again and again, but animal fleas don't like people so they don't feed a long time or make big bites.

There is also a condition called scabies...tiny bites like this.
But they tend to itch like mad. Not all scabies mite bites get inflamed. Some people are more allergic than others in this regard.
Chiggers are another possibility...
http://www.google.com/search?q=flea+...%3B2403%3B1899

But as a rule they itch alot. You can pick up chiggers on the legs and ankles, and they move to where the skin is softest to bite.
Walking thru leaves, or getting sand in shoes may bring them.
People vary in response to chigger bites....some get big welts and others not. They fade within a week or so.