Hi Ranganathan, Welcome to HealthcareMagic Forum.
Was he of the same build since you saw him or you feel has he lost weight recently? His BMI is 15.3 which means he is underweight
secondary to Malnutrition
which could be due to various factors as u said Depression
. His Hemoglobin
is also fine, may be he is not taking his food Properly due to some mental tension which is going on in his mind may be for months. You should be taking him to a Psychiatrist
at the earliest if you feel he is depressed as he will need counseling and medications else you can take him to a Physician as he needs to be examined physically. Once the cause is cured his appetite will improve and he will start putting on weight and become well nourished.