on the face of it, I would say "poor little mite " :( ,
but from my own experience it might not be as straight forward as it looks, theres been many an occasion when my own DD has gone to School looking pale with panda eyes, & often times she suffers diareah at School, sometimes sent home too, so I'm sure for the parents that don't know her situation it can look very suspect & I can imagine they could complain in the same way you do
BUT, she has ongoing health problems, that flare up from time to time, sometimes ongoing, & unless very very bad, we have to manage it the best we can & she has to go to School regardless or she would just miss to much, the School know the problems & work with her on it with rest time etc, & call me to collect her only if its really bad
Its possible there are other factors you don't know with this Child, even something such as a known & now passed source of food poisoning, or he was sick due to another none contagious health problem