Hi,I had gone through your query and understand your concern.
No,hemorrhoid is very unlikely.
It is most likely due to strain during defecation causing injury to anal mucosa.For this you need not to worry.Please add fiber(vegetables) in his meal to avoid constipation
and for smooth bowel movement.
But if blood passes again and fever,abdominal pain
develops ,then bacillary dysentery
is a possibility which needs to be treated with antibiotic.
So my suggestion is:please observe another 2 motions and if blood in stool
continues,then meet your local doctor. Otherwise stay relax.
Hope this helps you.
Wish your son good health.