The child does seem to have suffered from Bacillary dysentry
in view of blood and so many pus cells in stool. It would have been better if he would have been given intra-venous antibiotics instead of oral and after such a severe bacterial gut infection in such a small child, lactose intolerance
usually does develop for which baby should be put on lactose-free diet.
I suggest you get a fresh stool routine examination done along with Stool pH and for presence of reducing substances in stool and then modify treatment accordingly. Good luck.